I have been on the Trunk Bay snorkle trip and I can only say it's just OK.. It's a nice outting as such, but I would not let it interfer with your shopping trip in to town.. The boat ride over to St. John is fun. And if you want to put snorkle gear in to your mouth that has been in about 4000 mouths of other people, and old gear that leaks, then that's great.. Like I say, it is an OK trip, but you will not come home jumping with joy about it.. Go to a sporting goods store and buy your own gear and take it with you..This way you will have a clean mouth tube and a mask with good, new rubber that does not leak.. Have fun.. OM
The last time I cruised with Carnival they had upgraded the snorkel gear to a packed gear in plastic wrapper that you purchase adn only you put in your mouth.
I went on a cruise to Cozumel once and I was grossed out by the people re-using the snorkel gear after it sat in salt water a few minutes. I think since people are aware of AIDS that Carnival decided it wasn't wise for them to recycle the snorkel gear anymore.