We rented a jeep just across from the ship docking. Went to Saphire Beach and snorkelled with our teenagers for a bit. Then went on to Corki(sp) Beach and Magden's beach. Much preferred Sapphire Beach to anything. It was the most beautiful scenery I have seen in a long time. And you didn't have to pay to get in.
That was all we did in St. Thomas.
Nothing in St. Maarten, we just walked to the beach and stayed there for the afternoon.