Didn't mention Belize, but if you go take the snorkle trip to Amberguie Cay. Pretty cool swimming with big Rays and Nurse Sharks. Nice boat ride and lunch served up on the little island (name?). Nice little shopping area there too for the little lady.
Roatan, took the snorkle tour on the far side of the island from the Cruise dock. Really nice beach and good food at the grass roofed cabanas. Couldn't snorkle because it was too windy, but supposed to be some of the best in the world.
Cozumel is really just shopping and drinking establishments, but my son rented a small motor scooter and rode it all the way around the island. He had a great time doing that.
Enjoy yourselves and don't eat too much (hard not to do)