Personally, I like to micromap. I’ve mapped individual trees, poles, benches, and trashcans, for example. I also like to map forested/scrub areas. Buildings themselves are also kind of fun to map, so long as I have the building plugin installed to JOSM.
It feels really cool to map landcover (forests, farmland etc) and then see how much better the map looks compared to the gray emptyness that was there before!
I’m also always adding and updating POIs when out and about. I like to use EveryDoor to when focusing on POIs. It’s really easy to add opening hours and a ton of other tags. Even if the tag is not cataloged/preconfigured in EveryDoor you can add tags manually really easily.