Emacsを深く使うにあたってはEmacs Lispを学ぶことは避けられません。
Lispレベルまで理解していれば、様々な問題に対して自分で解決できますし、自分が欲しい機能を自分で実装できたりするからです。

elispを深く学ぶには、infoマニュアルや拙著Emacs Lispテクニックバイブル 〜真髄を知るLispの掟〜 を通読するのもいいですが、やはり実際のソースコードを読んで実行して理解するのが早道です。
では、どのようなコードを読めばいいのかというと、全体像を理解できるくらいの短いコードを読めばいいです。

そこで、僕の手持ちのパッケージからソースコードの短い順でランキング付けしました。
僕はquelpa でパッケージを管理していますが、el-getの方は以下のスクリプトで ~/.emacs.d/quelpa/build → ~/.emacs.d/el-get の置換をすれば動きます。

ここでいう「行数」とはソースコードの実行数であり、行単位のコメント(先頭行が;)と空行を除いたものです。
行数が一桁のものはrequireとprovideでオシマイなので、10行以上のものを選択しましょう。
50行以内のパッケージもそれなりに多いので学習の助けになるでしょう。

sudo-edit.elは6行のコマンドが2つだけというごく小さなパッケージなので理解はたやすいです。
逆に、こんな短いものであってもヘッダを書いて所定の手続きを踏めば MELPAに登録されるので、便利で安定している自作コマンドがあるならば思い切ってMELPA登録申請してみましょう。
MELPAへのパッケージ登録はelisp初心者でもできるのです。

なお、この記事はorg-babelの実行機能を使っています。

結果

def code_lines(el)
  File.read(el).force_encoding("binary").lines.grep(/^[^;]./).length
end

Dir.chdir File.expand_path("~/.emacs.d/quelpa/build/")
pkgs = Dir["*"]
els = pkgs.map{|d| "#{Dir.pwd}/#{d}/#{d}.el"}.select{|el| File.exist?(el)}
[["行数", "バイト数", "パッケージ名"], nil].concat(
  els.map{|el| [code_lines(el), File.size(el), File.basename(el,".el")]}.sort)
行数 バイト数 パッケージ名
1 308 python3-info
2 48 solarized-theme
2 56 apropospriate-theme
2 2692 google-translate
3 408 boon
4 255 noctilux-theme
5 1053 gh
8 8203 multiple-cursors
13 1870 sudo-edit
13 1928 dedicated
14 2151 wgrep-ag
15 1902 helm-filesets
16 2045 dired-imenu
17 1292 cd-compile
17 2133 date-at-point
19 2207 gitignore-mode
20 2073 hookify
22 1371 ob-browser
24 2359 howm
25 2236 esh-buf-stack
25 2675 dired-sort
25 2909 ido-occasional
25 3290 switch-buffer-functions
26 3424 roguel-ike
28 1702 subshell-proc
28 2766 realtime-preview
29 2234 request-deferred
29 2651 ruby-hash-syntax
29 2754 pmdm
31 1750 oniisama
31 1757 color-theme-solarized
33 3327 omni-scratch
33 3339 ibuffer-tramp
34 2592 cbm
34 3047 easy-repeat
35 2266 css-eldoc
35 2280 pastelmac-theme
35 3016 better-defaults
39 4850 recentf-ext
40 3664 morlock
41 3042 idomenu
41 3742 phi-search-migemo
42 2454 sudden-death
42 3386 man-commands
42 3596 unify-opening
42 4930 echo-bell
43 2950 verify-url
43 3174 ido-describe-bindings
43 3239 twilight-theme
43 3822 prompt-text
44 2771 helm-hoogle
44 3069 fic-mode
46 5100 backup-each-save
46 6050 open-junk-file
47 3155 define-word
47 3284 zzz-to-char
48 3172 scratch-pop
48 3191 bitly
49 3228 drill-instructor-AZIK-force
49 4186 unkillable-scratch
49 7183 term-alert
50 2316 backtrace-mode
50 3322 arjen-grey-theme
50 4431 ace-jump-helm-line
51 3133 logito
51 3327 termbright-theme
51 3402 headlong
52 3491 real-auto-save
52 7179 wimpy-del
52 8330 expand-region
53 4139 dim-autoload
53 4360 path-headerline-mode
54 3317 phi-search-dired
54 3446 guru-mode
54 3983 paredit-menu
54 4517 outlined-elisp-mode
54 4937 smart-cursor-color
55 2549 ob-translate
55 4496 codesearch
55 4980 yatemplate
56 3665 hl-todo
57 2278 sane-term
57 6265 sticky
58 3423 tab-jump-out
59 4147 init-open-recentf
59 4527 helm-mode-manager
59 4690 linum-relative
59 8975 dired-details+
60 3985 bury-successful-compilation
60 4024 darkmine-theme
60 4376 seeing-is-believing
60 4703 easy-escape
60 5909 filesets+
60 6507 sequential-command
61 3679 helm-package
61 3682 atom-one-dark-theme
61 4265 dired-avfs
62 4693 elscreen-persist
62 4957 avy-zap
63 4404 repeatable-motion
63 4718 flycheck-color-mode-line
63 7387 term-cmd
64 4083 scratch-palette
64 6996 helm-migemo
65 3382 abyss-theme
65 3520 org-doing
65 5264 railscasts-theme
66 3331 dired-toggle-sudo
66 5282 map-regexp
66 5585 page-break-lines
66 6866 waher-theme
67 4195 helm-chrome
67 4802 ctags
67 5196 sync-recentf
67 5784 green-phosphor-theme
67 5790 autumn-light-theme
67 5867 goto-last-change
69 5094 hemisu-theme
70 4172 relative-buffers
70 4420 ido-springboard
70 4780 0blayout
71 4649 helm-firefox
71 4859 watch-buffer
71 6871 hide-lines
72 4585 busybee-theme
72 5249 chinese-word-at-point
73 4179 eshell-did-you-mean
73 4733 system-specific-settings
74 3430 ace-jump-zap
75 4218 esh-help
75 4447 narrow-reindent
75 5548 myterminal-controls
76 4222 replace-symbol
76 4310 passthword
76 4484 ido-occur
76 4619 ido-at-point
76 4955 isearch-dabbrev
76 5137 term-run
77 5101 buffer-flip
77 5843 per-buffer-theme
77 6062 md-readme
77 6992 colonoscopy-theme
78 5112 shelltest-mode
78 6214 django-theme
78 7886 ubuntu-theme
79 5560 rand-theme
80 3775 expand-line
80 4402 helm-wordnet
80 5775 sunny-day-theme
80 6431 save-visited-files
80 7085 boron-theme
80 7193 bliss-theme
80 7241 dark-krystal-theme
82 5583 restart-emacs
82 7289 firecode-theme
83 4997 pandoc
83 4998 package-utils
84 4619 org-bullets
84 5301 shut-up
84 6264 highlight-leading-spaces
84 8141 nav-flash
85 7425 peacock-theme
85 7434 lavender-theme
85 7502 flatland-black-theme
86 5463 cycle-themes
86 5662 professional-theme
87 5001 gitconfig-mode
88 4548 espresso-theme
88 5277 highlight-thing
88 5312 vc-auto-commit
88 5365 ietf-docs
88 5971 smart-newline
88 6598 auto-complete-pcmp
89 4795 scratch-log
89 5154 gitty
90 4247 eshell-autojump
90 6344 ir-black-theme
91 5978 cl-lib-highlight
92 4577 ac-mozc
92 4853 iterator
92 5150 centimacro
92 5299 discover-my-major
92 5385 openwith
92 8787 org-password-manager
94 5939 github-browse-file
94 6239 xah-replace-pairs
94 6787 soft-morning-theme
94 12366 hl-line+
95 6889 seoul256-theme
96 4924 simple-call-tree
96 5372 beginend
97 5264 mwim
97 6901 paper-theme
98 5058 markdown-mode+
98 5238 shrink-whitespace
98 12097 clues-theme
99 6009 shell-split-string
99 6369 badwolf-theme
99 6817 dired-narrow
100 6349 elscreen-multi-term
102 5489 cyphejor
102 6136 cursor-test
102 14699 diminish
103 7486 pretty-symbols
103 8174 bubbleberry-theme
104 4300 rotate
104 5489 golden-ratio
104 6094 describe-number
105 6194 helm-flx
105 6548 fm
106 7020 multi-compile
107 13577 faff-theme
107 28083 ace-pinyin
109 6801 delim-kill
109 6822 orglink
109 7210 eclipse-theme
109 10150 pp+
109 11364 hide-comnt
110 6136 smarty-mode
111 6282 inflections
111 7216 column-enforce-mode
112 5925 google
112 9777 atom-dark-theme
113 7773 ibuffer-vc
114 5698 smartchr
114 6874 highlight-defined
115 6590 smart-tab
115 8794 exec-path-from-shell
116 6410 find-temp-file
116 14321 narrow-indirect
117 6094 helm-company
117 6567 diffview
117 8119 inkpot-theme
117 8285 idea-darkula-theme
118 7186 springboard
119 6815 sublimity
120 7698 molokai-theme
121 6368 helm-bm
121 8196 dired-toggle
122 5991 spaces
122 7715 gandalf-theme
124 5890 noflet
124 5979 letcheck
124 6556 smartrep
124 6756 chruby
124 6970 projector
124 8965 borland-blue-theme
125 6660 lice
125 6711 string-inflection
125 7093 ace-popup-menu
125 29592 tinysegmenter
126 5066 ansi
126 9969 iodine-theme
127 7311 helm-flycheck
127 8358 caroline-theme
128 6450 multifiles
128 11329 pp-c-l
130 8078 cherry-blossom-theme
131 7746 comment-dwim-2
131 9801 load-relative
132 7118 org-toc
132 7330 ido-clever-match
132 8272 hideshowvis
132 8429 dired-open
132 9783 phi-search-mc
132 10131 darcula-theme
132 12300 pangu-spacing
134 6352 ace-jump-buffer
134 6941 dired-hacks-utils
134 7836 paren-completer
134 8025 xah-lookup
134 8346 show-marks
135 5628 firebelly-theme
135 7359 pallet
135 9045 find-file-in-repository
137 7919 olivetti
137 8001 ace-isearch
138 8349 hiwin
138 11030 hl-defined
139 5944 slack
139 8102 checkbox
139 8575 dired-single
139 15400 key-chord
140 6056 org-wc
140 7734 jaword
140 7791 org-eldoc
141 5254 jaunte
141 7753 free-keys
141 9366 orgit
143 7943 dash-functional
143 16802 keydef
144 6364 git-lens
145 7199 uimage
145 7850 omni-kill
145 7931 furl
146 8076 pcache
146 8684 http
146 11124 calmer-forest-theme
147 9361 birds-of-paradise-plus-theme
148 6251 edit-at-point
149 8509 dizzee
149 9703 auto-shell-command
150 6867 ob-http
150 8384 hungry-delete
150 11027 ahungry-theme
151 8387 visible-mark
151 8817 download-region
152 7644 stash
152 7982 autobookmarks
152 9921 phi-search
152 12020 auto-save-buffers-enhanced
153 7971 org-present
153 8465 highlight-stages
153 8543 ac-skk
154 10667 ujelly-theme
154 10686 debug-print
156 7215 @
156 8802 gntp
156 10503 rich-minority
156 11905 iflipb
157 7284 mbe
158 7653 smart-compile
158 9015 nyan-mode
158 9533 eldoc-eval
158 10330 light-soap-theme
160 8702 tabula-rasa
161 9843 psession
161 10186 dired-details
162 8677 punctuality-logger
162 12107 distinguished-theme
163 8722 firestarter
164 7122 number
164 8315 imenu-list
164 12749 planet-theme
166 8124 smeargle
166 8506 yandex-weather
167 8289 git-link
168 8264 autotetris-mode
169 7916 anyins
169 9331 helm-commandlinefu
169 9483 window-numbering
169 10001 imenu-anywhere
169 10290 dakrone-theme
170 9420 ido-migemo
170 9685 helm-descbinds
170 9989 windata
170 10042 kill-or-bury-alive
171 11835 ctags-update
172 9099 rake
172 15859 cursor-chg
173 8051 itail
173 9078 sclang-extensions
175 8803 jazzradio
177 8077 yafolding
179 7560 ruby-block
179 9343 fold-this
180 13705 findr
181 8422 swap-buffers
181 9276 elmacro
182 8694 helm-google
182 10408 loccur
182 10562 ido-completing-read+
183 7723 general-close
183 9071 org-multiple-keymap
184 9106 switch-window
184 11356 elscreen-separate-buffer-list
185 9301 clocker
185 9703 focus
185 10413 pc-bufsw
185 12591 rainbow-delimiters
186 9072 splitjoin
187 7861 string-edit
188 7953 git
191 11632 badger-theme
191 12829 broadcast
191 14691 toc-org
192 9415 cdb
192 11151 package-safe-delete
193 10638 eshell-prompt-extras
194 9826 smart-shift
195 11588 org-drill-table
196 11242 relative-line-numbers
196 11323 highlight-blocks
197 9991 flx-ido
197 12325 organic-green-theme
198 11664 emoji-cheat-sheet-plus
198 12543 el2markdown
199 18044 req-package
200 8748 undohist
201 9847 zlc
202 8501 ht
202 9778 zop-to-char
203 8846 bpr
204 11451 indent-guide
204 13760 persistent-soft
205 10781 flex-isearch
205 12088 pkg-info
206 11716 auto-yasnippet
206 12279 bind-key
207 9590 uzumaki
207 13932 melpa-upstream-visit
208 11926 writeroom-mode
208 13516 goto-chg
209 18324 gruvbox-theme
210 14172 warm-night-theme
211 14713 white-sand-theme
212 10157 drag-stuff
212 12039 rainbow-identifiers
213 8837 thingopt
214 14463 oldlace-theme
214 14781 showkey
215 14398 hamburg-theme
215 15077 reykjavik-theme
216 15165 greymatters-theme
218 14881 phoenix-dark-pink-theme
225 22404 embrace
229 9240 vim-region
229 12616 jump-char
229 14055 cloc
229 16199 el-autoyas
231 13422 c-eldoc
231 13966 auto-capitalize
233 10816 pcsv
233 13448 anything-replace-string
233 14998 owdriver
234 11806 ample-regexps
234 12817 nodejs-repl
235 12565 jump
236 10455 mpv
237 11353 async
237 11590 shell-pop
237 13348 ido-vertical-mode
238 11078 quickref
238 11141 dired-k
238 13776 magit-gh-pulls
241 12673 wrap-region
241 23411 clipmon
242 12040 yascroll
242 12445 camcorder
244 17051 rope-read-mode
245 12037 rect+
246 13794 corral
247 13695 test-simple
254 15937 niflheim-theme
256 13844 shell-switcher
258 11400 vline
259 13411 helm-ag-r
259 16709 simpleclip
260 12651 flx-isearch
262 13078 ert-runner
262 13246 flx
265 14152 ob-ipython
265 14417 edit-indirect
266 13166 imenus
270 11797 stripe-buffer
271 16853 gruber-darker-theme
272 14394 shackle
275 13572 vlf
276 14168 save-sexp
279 11717 electric-spacing
279 17189 centered-cursor-mode
280 14865 aggressive-indent
281 10673 quick-buffer-switch
282 15653 kurecolor
285 13903 haskell-emacs
287 14668 eshell-z
288 13525 helm-perldoc
288 15148 helm-dash
288 15187 yaml-mode
288 15882 initsplit
288 17648 buffer-stack
289 13364 speed-type
290 15866 helm-open-github
292 13244 garoon
292 16016 magit-gitflow
292 19394 helm-c-yasnippet
297 13089 git-rebase-mode
297 19099 zerodark-theme
299 14456 tabulated-list
301 12353 ace-link
302 21700 airline-themes
303 15732 operate-on-number
306 17912 howdoi
307 15355 ido-hacks
310 17921 highlight-symbol
311 29347 jbeans-theme
312 14321 tracking
314 19525 yaxception
319 16520 anaphora
322 16051 avy-migemo
322 24661 sr-speedbar
324 16238 fancy-narrow
326 18431 splitter
327 15914 annotate
329 20242 google-this
330 16467 discover
336 18789 pcomplete-extension
337 26820 moe-theme
349 17950 helm-ls-git
349 22516 outline-magic
352 16136 keyfreq
359 21168 visual-regexp-steroids
363 25713 guide-key
364 30981 plan9-theme
365 17298 state
365 24961 demo-it
371 17223 use-package
373 39987 lacarte
374 20405 symon
375 20934 helm-cmd-t
381 17856 smex
384 17941 esup
384 34405 darktooth-theme
388 18168 commander
388 19726 sunshine
390 18050 concurrent
390 18265 helm-ag
391 19301 mag-menu
391 24019 smooth-scroll
391 27850 basic-theme
396 17523 seq
398 19493 link-hint
399 21189 lisp-extra-font-lock
402 17483 ace-window
402 18427 diredful
402 19660 quelpa
405 16830 metaweblog
413 19009 yari
414 19701 image+
416 16406 f
418 58159 soothe-theme
422 22006 html-to-markdown
424 26483 jg-quicknav
426 17122 electric-operator
431 24827 el-init
433 21679 key-combo
433 22260 eval-sexp-fu
435 26121 on-screen
437 19882 powerline
438 21683 eyebrowse
439 21630 ag
439 23710 jist
440 24751 log4e
445 21228 polymode
446 20471 bbyac
446 20709 boxquote
447 22033 makey
452 22373 linked-buffer
456 25500 epl
462 30209 flatui-theme
464 34405 assess
464 34794 sisyphus
466 22123 runner
482 19681 s
488 32394 multi-term
492 24467 swoop
500 27315 org-journal
503 32720 multicolumn
505 26521 color-identifiers-mode
510 25306 git-commit-mode
512 33678 afternoon-theme
519 25729 keymap-utils
519 28252 origami
520 33229 log4j-mode
525 33209 grandshell-theme
526 34973 spacegray-theme
533 37235 back-button
544 27639 inf-ruby
552 26597 ov
563 25977 org-grep
568 31299 with-editor
574 26460 gist
575 27712 dired-subtree
579 38533 ample-zen-theme
582 23894 mew
582 28431 naquadah-theme
590 26913 smartwin
596 30497 eww-lnum
601 25740 yagist
607 30052 gotham-theme
612 38594 decl
612 41128 button-lock
613 28190 full-ack
613 43094 hexrgb
614 29154 poporg
615 35086 revive
616 30754 cycbuf
621 42107 cyberpunk-theme
628 30273 org-gcal
630 26062 swiper
635 28413 id-manager
637 33617 m-buffer
647 37592 xml-rpc
652 36187 litable
654 29280 ox-reveal
655 25214 subatomic-theme
659 34918 window-layout
665 47691 ample-theme
669 30540 anzu
670 29509 migemo
671 35249 pos-tip
672 39611 color-theme-sanityinc-solarized
674 29989 orgtbl-aggregate
674 36598 helm-projectile
677 32450 perspective
680 34810 minesweeper
683 36889 escreen
684 44482 wiki-nav
685 29385 shelldoc
685 31325 bog
695 46948 material-theme
711 43863 hardhat
716 40309 color-theme-sanityinc-tomorrow
718 39570 ido-ubiquitous
720 33122 easy-kill
720 33657 ack-menu
721 45934 el-get
723 34277 cask
723 41469 anything-complete
725 33821 anything-project
731 45249 macrostep
736 42638 dtrt-indent
738 33040 git-gutter
740 51606 leuven-theme
744 38380 list-utils
747 35388 hl-anything
749 41290 alert
769 35482 deferred
779 58643 auto-install
780 47303 ignoramus
782 51933 flatland-theme
789 33542 direx
793 36052 fcopy
803 38576 worf
808 43093 ace-jump-mode
817 44855 visual-regexp
826 35481 wgrep
834 52337 lentic
845 37871 hydra
861 42732 lusty-explorer
872 35792 neotree
873 39124 yabin
885 58100 aurora-theme
888 62118 hc-zenburn-theme
892 46232 websocket
892 46368 zencoding-mode
900 50568 dired-filter
907 43787 popwin
925 51625 emojify
945 44606 ox-pandoc
962 46719 org2blog
962 59249 anti-zenburn-theme
967 63350 win-switch
976 41085 avy
978 44203 enh-ruby-mode
996 47836 browse-kill-ring
998 69667 darkburn-theme
1010 51733 bm
1017 49134 helm-gtags
1040 49512 rust-mode
1041 71206 zenburn-theme
1045 52312 request
1077 57148 paxedit
1102 49916 names
1107 44565 prodigy
1110 63929 pophint
1125 53368 auto-highlight-symbol
1153 60290 which-key
1172 55381 quickrun
1174 55117 omnisharp
1203 77311 smart-mode-line
1208 56302 php-mode
1217 72410 simple-call-tree+
1218 61343 persp-mode
1232 55213 popup
1259 56487 summarye
1263 59742 weblogger
1266 59229 go-mode
1286 67877 color-theme
1299 68575 package-build
1321 65668 helm-swoop
1329 78074 yaoddmuse
1352 74816 pandoc-mode
1355 58673 ruby-mode
1370 63511 elscreen
1403 99859 isearch-prop
1447 101625 palette
1487 68980 outorg
1517 73728 tabbar
1529 97029 windows
1552 76415 lua-mode
1605 73503 ctable
1622 140690 highlight
1738 105641 alect-themes
1775 79298 workgroups
1812 74661 auto-complete
1837 78758 counsel
1855 87318 mediawiki
1864 98746 navi-mode
2046 84739 dash
2070 114254 font-lock-studio
2102 119281 pcre2el
2206 108569 projectile
2242 105312 company
2242 115266 org-toodledo
2275 111957 rebox2
2430 131710 gnuplot
2492 121698 paredit
2714 128944 org-drill
2782 113501 ivy
2791 160928 outshine
2871 169639 csharp-mode
2988 136032 circe
2998 118721 yatex
3080 171320 undo-tree
3177 179932 anything
3343 133789 imakado
3504 139280 emmet-mode
3733 188891 yasnippet
3966 164902 japanlaw
4287 365774 ucs-utils
4444 198364 monokai-theme
4910 236912 helm
5103 205259 skk
5232 289703 markdown-mode
6104 286725 slime
6125 289642 flycheck
6908 329671 smartparens
9428 431968 bongo
10450 422668 web-mode
10519 421135 w3m
11004 501553 js2-mode
11426 466886 twittering-mode

本日もお読みいただき、ありがとうございました。参考になれば嬉しいです。