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’s something I do when I’m out in crowded areas. It helps take my mind off people and gamify being outside. I try to map everything in the area with street complete.