When you're poolside, sandwiches are an easy-to-make and portable snack. Get as gourmet as you want with a deli platter featuring turkey, ham or whatever cold cuts you like. Add cheese, lettuce, tomato, condiments, pickles -- whatever you want -- so everyone can tailor them to their liking. For vegetarians, fresh mozzarella and tomato sandwiches are a perfect pair.
Want to put even less work into sandwiches? Peanut butter (or other nut or fruit butters) and jelly are still a no-cook, year-round staple that everyone loves.