For an all day trip to Caye Caulker I like Hustler Eco Tours catamaran package: Leave at 9:00 AM - snorkel Hol Chan & Shark and Ray Alley with lunch at a restuarant of your choice on Caye Caulker. After the last snorkel the beer and rum come out. You are back by 4:30. All this on a sail boat so no noisy, smelly motors.
Matthias and Frank and one other local make up your fun crew.