I ca n tell you what NOT to do.. Do not try the Ticket to Paradise tour. It was one of the worst tours we've ever been on. It was so bad in fact that several of us from the ship chipped and took a cab back to the town rather than attempt to stay there.
Do try the wonderful beach at the Westin Hotel, the best way to get to the hotel beaches is by bus. They have a great little bus system there for $1 50 cents for a transfer to get back. This is also a great and inexpensive way to tour the island.
We also went on the turtle encounter snorkel and it was wonderful. Whatever you choose to do have a lovely cruise.