In the light of massive scale of recent cyber-warfare I decided to take a few precautions. It's no secret that modern IT infrastructure has become ridiculously centralized in the last 20 years, and we saw in November 2020 what kind of global mayhem even a partial AWS outage can cause. And as we can see today, cancel culture can scale to entire countries. Reducing dependence on global corporations that answer to no one is always a good idea.
What's worth having backed up in case of a disaster? Some music and movies won't hurt but it's not crucial - these I'd expect to be shared via DVDs/Blu-Rays/portable drives, just like before Internet. It's the things we take for granted that matter: Wikipedia, detailed maps, dictionaries, software repositories.
I'm not too concerned about software repositories - there are 18 official German mirrors of OpenSUSE (though it's a shame that USA has more listed mirrors, it's a German distribution after all), and I don't install new packages that often. But what about the rest?
The solution for Wikipedia and Wiktionary is Kiwix. The whole English Wikipedia takes up less than 100GB of disk space. Both search by page title and full-text search are quite snappy. The catch is that all pictures are heavily down-scaled, and there's no JavaScript functionality such as sorting tables by non-default columns.
As for maps, there are excellent offline OSM-based solutions: Organic Maps for smartphones, and OpenMapTiles for the browser. The latter creates vector tiles, which use less disk space than raster tiles, and delegate styling to the browser. It's probably a bad idea to attempt to generate tiles for an entire continent unless you have a very beefy server, but making a self-hosted map for your country of residence from a source .osm.pbf file (download it from Geofabrik) doesn't take too long, all you need is 4-8 GB of RAM, an SSD, and a bit of patience.
A positive side-effect is that I can now keep the broadband modem turned off most of the time, using it only for weekly software updates. Not only does it save some 100 kW·h per year, but it is also the Internet diet promoted by Taleb, all the more relevant now that news diligently obey "The Basic Principles of War Propaganda". The rationing mechanism is the mobile data limit, set in the hotspot settings.