Well, Frase, you'll be leaving a week before us. We're going snorkeling in all of those ports. However, everyone doesn't like snorkeling. Grand Cayman-Stingray City, Seven Mile Beach, and someone recommended Rum Point (haven't been there personally). Cozumel-Chankanaab Park, Swim with the dolphins, Paradise Beach, Tulum, Xel-ha, Carlos n Charlies, Senior Frogs. Belize-sorry, only done snorkeling there. Roatan-only done snorkeling there, too. Tabayanna Beach was highly recommended. We did go through town a bit, didn't see much for shopping, though.
Have a marvelous cruise and save some sunshine and warm weather for us!