If you're taking a cooler, I assume you'll have your car nearby. Not many people take a cooler while backpacking.
So bring frisbees, swim gear, snorkel gear, radios, a good book to read, sunscreen, bikes if there's any place nearby to ride, hiking gear, and trail maps so you (hopefully) don't get lost.
So bring frisbees, swim gear, snorkel gear, radios, a good book to read, sunscreen, bikes if there's any place nearby to ride, hiking gear, and trail maps so you (hopefully) don't get lost.