Thanks, that helps to know what you enjoy.
Barbados-Tiami Catamaran sail/snorkel. Their cats are immaculate, the crews have been great, they take you to snorkel with the turtles and then to a nice beach break for rum punch. The Folkstone Underwater Marine Park is a nice snorkel, too. There are the salt mines and if you like spicy food, try the Bajan pepper sauce. It's hot but wonderful.
St. Lucia-pitons snorkel, Pigeon Island, or a "best of" tour.
Antigua-go outside of the terminal and negotiate with one of the drivers. We found one that took us to Shirley Heights, the harbour, and a nice beach with a restaurant/bar for $25/pp. There are 365 beaches, so you really can't go wrong. We did a snorkeling excursion once, but couldn't enjoy it for all the jelly fish in the water. Might have been the wrong time of year.
St. Maarten-Maho Beach, Orient Beach, Marigot, shopping, or take the water taxi to the beach near the port. We did the TikiHut snorkel the last time we were there and it was a great excursion.
Hope this helps some.