Graduation parties are big here, however, I don't know anyone who issues invites to anyone and everyone. We just had DDs graduation party on Sunday. We had about 50 people - friends and family. DD was pretty selective in who she invited. She received a selection of gift cards, cash and checks. Checks were in the $50 range which is a very common amount. For our family, well, DD has been giving $25 gift cards to most people, though we did give $50 each to her boyfriend and her best friend.
I find it supremely tacky to ask people to bring food, particularly if a lot of the people you are inviting you barely know. I love to plan parties, and I'm of the opinion that if I host a party, I have a responsibility to provide the food and drink. For DDs party, we had a friend who owns an Italian restaurant cater it as he gave us a break. If we didn't have that option, we would have grilled or something. But, we never would have asked people to provide the food.