Listen to music? Talk? Pass a joint around? Those that played instruments brought them and would jam.
I know I'm getting old and was kind of a prole but most parties that I went to in Atlantic Canada were like that, you brought what you could afford and the people holding the party provided the venue.
You had strangers at the party because friends would invite their friends who'd bring some other friends. One never knew if the party would be huge or a bust.
We were relatively poor students so food wasn't common unless people kicked in for a pizza or went out for donairs, whatever was plentiful and cheap and easy.
The worst parties usually involved alcohol, I spent New Years Eve (1989) cleaning a walk-in kitchen pantry at a friend's flat because my then-girlfriend had barfed in it after she ran to what she thought was the bathroom. I was a bit disillusioned with parties after that.
I'm not young (38), but my parents used to throw these kinds of open parties all the time when I was growing up. We had an open door policy, too, where anyone who showed up around a meal time was automatically served, too, and that provided a really awesome opportunity for us to build and strengthen friendships (being older and more worldly now, I know this is pretty common in large parts of the world, but it wasn't in central Virginia in the early 80s). We had a couple acres, and our house parties ranged from just a couple of folks over to hang out to large outdoor events with up to about 250 folks. In those cases it was always friends-of-friends-of-friends. As mentioned elsewhere, my family provided the venue and some general amenities (some drinks, core food) but it was expected that attendees would bring something to contribute.
As adults now, my wife & I try to have friends over regularly, too, but it's a lot more complicated in suburban US because of dual-income households, kids that either don't go to neighborhood schools or are involved in lots of extracurriculars, and generally antisocial neighbors.
You know, making music sounds great. I host "parties" on a regular basis, but they're small, I know almost everyone, and we usually play boardgames which I guessed most people wouldn't do at a party in the 80's :)
