I'm hosting the party this year for the 4th time in a row, and our staple has been pizza. I get the "Crowd Pleaser" deal from the local supermarket: 10 unbaked large pizzas, a variety of toppings. We just leave the oven on and throw a pizza in whenever someone wants one. There's always leftovers, even though last year I had about 40+ people here.
My guests bring dips, chips, cookies, desserts, vegetable trays, and beers of their choice.