St. Thomas - seriously check into the beaches over on St. John Island - one of the best ways to do it is to book the Champagne Catamaran sail tour. If you want to do it on your own you have to take a ferry from St. Thomas and then a cab to the beaches - go to www.vinow.com
for ferry schedules and beach information. One of the best beaches on St. Thomas proper would have to be Sapphire Beach - very pretty, good snorkeling. SHopping in St. Thomas - either at Havensight Mall -where you will most likely dock or in downtown Charlotte-Amalie. There are birds and botanical gardens up on Paradise Point in St. Thomas - short tram ride up the mountian, you can walk to the tram from the ship.
Grenada - "The Spice Island" take an island tour that includes the spice plantations.