Whatever happened to slumber parties where you just listen to records and talk about boys and braid each other's hair? Just do the same things every small group of friends does: Talking, making or listening to music, going to concerts, watching movies/TV, playing games (any kind), cooking/sharing a meal. And booze, if that's your thing.
I've been thinking recently that hosting semi-regular movie nights with friends sounds like a nice idea. Maybe you can host a themed event. One for terrible films or music, where everyone agrees on a terrible movie to watch, or brings all the worst albums they can find and plays selections from them (FYI, I stole that last idea from a local bar). You could also go camping or explore abandoned buildings or something along those lines if you're interested in something a little different. Day trips to strange/remote places can be an interesting experience.
I went to an "introverts party" once (as if three people together in a room can be considered a party) where we just read books independently… 😕 I got baked beforehand and couldn't even focus on whatever I was reading. But it was still a decent time as far as small gatherings go.
