A potentially very useful feature less trivial to implement than mere
bundling of entertainment and encyclopedic content would be a routing service
requiring only a one-time download of geoinformation and map tiles for a
locality you choose – OSM already lets you do this[1] – and from then on
doing all route calculations offline, using this previously downloaded data.
A bit like what car navigation devices do, but free and without satellite
navigation, instead just giving you a zoomable map and/or a sequence of
driving instructions for each fork in your path. This doesn't sound like
rocket science, yet I'm not aware it exists, free or unfree.
Simple hoarding of content for later offline use is probably something many
people have individually done, however unlikely they were/are to actually
lose internet access. For me, having a hoard relevant to my interests turned
out to be useful when I found myself more or less unable to properly use the
web for many months. Also useful because content disappears from the web.
[1] https://wiki.openstreetmap.org/wiki/Planet.osm#content
