I just took a family vacation to Key West. We spent most of the time by the pool but did some exciting things too- renting mopeds, paddle boarding, drinking coconut water straight from the fruit. We saw Ernest Hemmingway's house, and more importantly the famous 6-toed cats who live there (which R29 calls one of the "Coolest U.S. Attractions You've Never Heard Of").
When I wasn't in a bathing suit (read: not often), I wore light, flowy dresses. My most summery items were best for the heat and casual vibes on the island.