My wife has thrown me a surprise birthday. I know about there's about 15 people going.
I haven't been able to workout the location yet. Yet, I know my wife, she's going to expect everyone to pay for themselves.
If I was going to an invited meal, I would be 50/50 about paying or not. If they pay, great if not, no problem.
My wife is cluleless with money, she won't have anything prepared. Not sure if I should be prepared to pay for everyone's meal or not?
If she specified on invitation whether they have to pay or not then she's fulfilled her social contract mate.
I however would always expect to pay for anything anywhere I go. That way, if I don't. Well, that's a pleasant surprise.