Manyverse might be good for that. It’s P2P social networking that syncs whenever you’ve got internet.
The entire suite of simple mobile apps is also really good, the Notes app in particular seems useful.
Organic Maps or OsmAnd will let you download maps offline and navigate with just GPS.
Aard 2 will let you browse an entire dump of Wikipedia and Wiktionary.
Shattered Pixel Dungeon is a great time killer. There’s a Lemmy community over at !pixeldungeon@lemmy.world