Great itinerary! I'll fill you in on some of my favorite places, but I'm sure you'll find some of your own.
Grenada: Grand Anse Beach is beautiful. Flamingo Bay is a fantastic snorkel. It's the spice island, so be sure to pick up some of your favorites. We also did an island tour up to the rain forest, which was quite nice. It took you by some beautiful homes, too.
Bonaire: Mushi/Mushi catamaran sail/snorkel is fabulous. There are a bunch of really local bars/restaurants right where you dock. Great spot to grab a beer and people watch. To me, Bonaire is not a really scenic island for a land tour, but there are a few points of interest if so inclined.
Curacao: Good shopping, nice land tours. Curacao is a picturesque island. The island tour that stops at the Curacao factory is an interesting tour. The snorkeling there is fair. They'll take you to a tug wreck.
Grand Turk: There's a shopping area and beach right where you dock. We did a 2 stop snorkel that was very good. One stop was for coral and one was for sea life, both of which were abundant and beautiful. They have some segway tours and also some atv tours that sound like fun, too. It's not a mountainous island, but it was very neat and clean before the hurricane.
Tortola: Great place for a land tour. We just negotiated with a cab driver outside the terminal area. We've also done 2 snorkel trips which both went across to Norman's Island, and they were both fantastic snorkels. They offer a tour over to Virgin Gorda and the Baths. That is a great tour as well.
St. Maartin: Loads of fun things to do there. The last time we were there, we went to the TikiHut for snorkeling. The vendors running it were so accomodating and friendly. They'd take you back to the ship or drop you at the shopping area. The shopping there is fantastic. There are tours to Orient Beach, which is an adult beach as there is an area that is nude. The ones that shouldn't be without clothing are the ones that walk the entire area, so just to let you know. There is also Maho Beach where the jets land on top of you.
Antigua: The last time, we negotiated with a driver outside of ther terminal. He took us over to Shirley Heights, then to the harbour, and then to one of the 365 beaches for a few hours of drinks, food, swimming and relaxing. The snorkeling was just ok, too many jelly fish for me.
St. Vincent: It's how the Caribbean used to be. They meet you at the dock with a local band and dancers. There's a little shopping area at the terminal. You can walk into town. We did a nice catamaran sail/snorkel there, too.
St. Lucia: One of my favorite islands. Decent shopping, great snorkeling-especially at the pitons, and friendly locals. The last time we were there, we went to Pigeon Island. They charged us $85/each way for the cab and charged us an entrance fee. There is a pirate ship excursion that goes there for $45/pp through the ship, so go with that excursion. They spent about an hour at Pigeon Island. There's a fort with a great view and some beautiful beaches. It too is a good island for a land tour.
Trinidad: We did the Angostura Plant/Botanical Gardens tour and really enjoyed it. Trinidad is a heavily populated island, it reminds me of New York with the subways and bus stations. The beaches are not that good because it is a huge oil area.
Be sure to try the Bajan Pepper sauce in Barbados. It's the only island you can find it. Oh, in Trinidad, try to find doubles. It's a local sandwich sort of like a empanada. It's made with chick peas and seasonings; mild, spicy or hot.
Hope this helps a bit.