What's an easy, inexpensive appetizer or dessert that I can make or buy to bring to a Friday evening beach party?

I live in a lake community and they’re having a Friday night “Cocktails on the Beach” party. They’re asking everyone to bring an appetizer or dessert. I want something easy that I can make or buy. I prefer not to spend more than $10 or $15. I can do a Thursday night Costco run or do some prepping, if necessary.