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.
I think this is actually one of the most important things to map to help with adoption of using OSM data as a daily driver! There are so many missing POIs.