You can't take your passports as you have to surrender nthem to
DCL upon check-in. Your nationality for the duration of the cruise is either Disney Magic or Disney Wonder
When leaving the ship you are offered to take towels from the ship, which you simply drop in a laundry basket upon return.
If you take your own snorkel-stuff make sure that you have it in a proper bag. We have a special divebag made of a mesh-like material to allow everything to dry.
All the guided tours offer snorkel equipment. I would advise you to take their's for your first time. Some people have problems with snorkeling and you have to pay about $100 for a good ABC-set (Mask, Snorkel, Fins). So better rent, and if you like it you can buy soem equipment for your next cruise
f you have never snorkeled before a guided tour with an instructor is best.
If you happen to be at WDW before the cruise you may want to go to Typhoon Lagoon. There's a snorkeling pool with lots of lifeguards who give you instructions. It's a controlled environment and a very good opportunity to get some practice.
If you tend to sunburn easily, you should bring a T-shirt with you to wear in the water: You can burn you back severely while snorkeling!!! You're in relatively cool water, but your upper back is most of the time above the surface and exposed to the Caribbean sun. You don't feel the sun's power due to the cooling water, but nevertheless you are exposed to agressive UV-radiation.
We usually just take some cash, a creditcard, our KTTW-cards and our German ID-cards (For you it would be DL). At Mickey's Mates DCL sells a nice waterproof container with a lanyard at a reasonable price - something like $6 or 7, which holds all aforementioned stuff. They KTTW-card and a photo-ID are mandatory!! The rest is optional. You may also get one of those containers at
Walmart or so for $2 or 3, but without a DCL-logo
We also take some water, a a set of clothes to change so that we can stay ashore and do some shopping after the snorkeling without having to go back to the ship for changing.
Do NOT take any food off the ship!!! It is stictly forbidden. Especially fruit will get you into trouble.