MeMondays was people introducing themselves with a pic and some info.
FapDayFriday was for posting porn you found recently. Just learned this is a SFW instance, so maybe not feasible here.
There were other weekly events, but I can only remember those and Tech Tuesday to talk about technology.
Videogames or cooking/baking. I've done a lot of bread baking but made a cake by myself for the first time for 4th of July.