*well, some important parts at least.
In a post apocalyptic world the job of rebuilding civilization is left to a few survivors. But theres no need to start from zero, give humanity a head start by keeping a couple copies of wikipedia around. You can download the entirety of wikipedia taking up less than just 100 gigabytes of data! Or a slimmed down mini version of wikipedia for just 10 gigabytes! It goes beyond wikipedia though, using Kiwix you can download all sorts of useful content, like WikEm the "world's largest emergency medicine open-access resource" or various videos from youtube.
In all seriousness I don't think I really need to explain the utility of having access to the most important parts of the internet while offline, whether in an emergency scenario or if your just away from internet access.
Note: if you are a doomsday preper you might be interested in this, and this video. They essentially go through making a really rugged "laptop" (a raspberrypi in a pelican case) with wikipedia and a bunch of useful information on (badass).
It's worth noting there is more than one way of doing this, essentially you download some software from kiwix and download some .zim files which are "highly compressed copies of entire websites", you can then view the websites offline with a similar experience to normal internet browsing using the kiwix software. (Below is a screenshot of the kiwix app with the wikibooks .zim file open).
Go to the download page of kiwix and download the appropriate version. They offer many versions, supporting platforms from android to macOS.
Somewhat annoyingly for the macOS and browser extension versions you cannot download the .zim files from within the application. If you download this google sheets spreadsheet from kiwix with download links for .zim files as a csv (comma separated values) file you can use this python code to filter through it and find what you want. (Or just use the output below).
Sources I want:
['Wikipedia', 'Wikibooks', 'Wikiquote', 'Wiktionary', 'Wikem']
The biggest from these sources:
{'Description': 'The free encyclopedia',
'Flavour': 'Full',
'Language': 'English',
'Source': 'Wikipedia',
'Title': 'Wikipedia',
'URL': 'http://download.kiwix.org/zim/wikipedia_en_all_maxi.zim',
'_size': '83107984'}
{'Description': 'From Wikibooks, open books for an open world',
'Flavour': 'Full',
'Language': 'English',
'Source': 'Wikibooks',
'Title': 'Wikibooks',
'URL': 'http://download.kiwix.org/zim/wikibooks_en_all_maxi.zim',
'_size': '4405230'}
{'Description': 'From Wikiquote',
'Flavour': 'Full',
'Language': 'English',
'Source': 'Wikiquote',
'Title': 'Wikiquote',
'URL': 'http://download.kiwix.org/zim/wikiquote_en_all_maxi.zim',
'_size': '607235'}
{'Description': 'Definition from Wiktionary, the free dictionary',
'Flavour': 'Full',
'Language': 'English',
'Source': 'Wiktionary',
'Title': 'Wiktionary',
'URL': 'http://download.kiwix.org/zim/wiktionary_en_all_maxi.zim',
'_size': '5920770'}
{'Description': "The world's largest emergency medicine open-access resource",
'Flavour': 'Full',
'Language': 'English',
'Source': 'Wikem',
'Title': 'WikEM',
'URL': 'http://download.kiwix.org/zim/wikem_en_all_maxi.zim',
'_size': '39695'}