Take a towel with you! You can sign for one onboard before you leave the ship. There are none available on the island. Be sure to bring it back onboard on your return and turn in your slip or you will be charged for it by the cruiseline. Also be sure and take your sunglasses and sunscreen with you. The sun is very intense and there are umbrellas but they do not really provide the protection you need. No need for bugspray so don't bother.
Bring along a disposeable underwater camera. There are a lot of fish and other marine life to see and take snapshots of.
