Don't know if you cruised yet but the last 2 times were were in St. Thomas we booked a tour with Godfrey Tours. Half the price of the ship's tours, you'll get a great tour of the island and/or they will take you to any beach you want to go to, leave you there and come back to pick you up in time to make the ship's departure.
We usually tour for 3-4 hours then go to the beach for a few hours. On one tour we were given drinks and food. You can look up Godfrey Tours on the internet and pre-book. They will have someone at the dock waiting for you when you get off the ship. The price is cheaper if you can get a group together. We had two vans of passengers last year @ $20 each.