Not trying to hijack this threat but wanted to offer another option for Tortola. Another excursion for Tortola is the the Baths at Virgin Gorda. We booked this excursion on our own because DS was too young to book with Disney. We ended up saving quite a bit too as Disney's prices were around $100/person and we did it for around $125 for all of us. It was so easy to do on our own too.
Anyway, we took a ferry from Tortola to Virgin Gorda (probably 20-30 mins). Then we boarded Taxis over to the Baths and then it was just a couple of bucks to get in. We explored the caves, went swimming and took some great pictures of fish. It would have been a nice little spot for snorkeling if we had gear with us. Also, there may have been a place to rent gear but didn't see it. Anyway, it was gorgeous! We've even talked about doing this excursion again if we go back to Tortola. It was the highlight of port time! Let me know if you'd like to see some pictures