We've had "semi" pot-luck situations in the past on Saturday night. That said, for those that put any effort into it, it really hampers the fishing on Saturday evening. i.e. most guys are fishing till dark (which doesn't happen till 9 or later in late May), then walking out, de-wadering, then having to drive back, and may not arrive at the pavilion till well after 10, depending on how far away they were fishing. So, if they have to make something, they gotta cut the fishing short.
In recent times it sort of died. Which is fine by me because I don't wanna feel guilty about not putting much effort into it, and I don't wanna lose fishing time either.
That said, yes, there's usually some food and drink being passed around Saturday night and EARLY Sunday morn. The rule is pretty much have the food and drink that you need and don't expect anything else, but don't be shy about taking offerings or offering to others, either. Somebody will pass around home-made hot pickles, or have a pot of chili, or chips and some fancy dip, stuff like that.
For first timers, note the typically late night for the main social gatherings. There are informal gatherings going on all over the campground at all times of the day and night, and seemingly always a few at the pavilion. Feel free to impose. Find a group somewhere, introduce yourself, and enter the fray. It's a pretty welcoming group overall.
But the centralized gathering is at the pavilion Friday and especially Saturday evenings. It gets going late and stays going late. If you show up at the pavilion at 9:00 to only a couple of guys, don't think it's over. It hasn't begun and the majority just aren't there yet. So don't skip out on the spinner fall at dusk in the name of getting back in time to socialize, you'll just beat most people back anyway. A few guys are always still trickling in at 11:00 p.m.! It's more crowded at 1 a.m. than it is at 9:30 p.m.