I'd make deviled eggs. Cheap, cheap, cheap, and they are always the first things to go.
If you haven't made them before, just make sure you boil the eggs ten minutes. No soft yolks. I don't get fancy with them, either. Just mayo and a bit of yellow mustard blended in the yolks. Easy, and you can make them ahead of time.
Get togethers can be even more fun (next time) if people bring a snack themselves, too--especially if they bring a favorite. Then you get something delicious to try, and you might even get a new recipe.
Lots of good suggestions from the other responders, too!