Seaduced/Seaduction is the snorkle/sunset cruise company I use whenever possible. They are friendly, knowledgable and very fun. Good cooks too! I've taken just about every trip they offer when I have guests in town.
As for dining-if you go to Casa Picaso don't forget reservations! Taste of Thailand is awesome too. Papi's is great home cooking at low prices, Blue Water is a popular tourist place-good seafood, a little expensive.
BC's on Sunday afternoon for BBQ, and Tuesdays for burger days!
All in all, you can't go too wrong here.