A bag of frozen cooked shrimp. Buy it now, keep it in your freezer, take it out when you get home to defrost in the fridge a bit, and the next morning bring it and leave it out to defrost the rest of the way. That and a jar of cocktail sauce makes a party.

Cheese and crackers and salami or sopprasetta won't need refrigeration from the time you leave the house in the morning till the party.