Hi Courtney6200, welcome to Cruise-Chat! Congratulations on your up-coming cruise! Just be warned, cruising is addictive
Cozumel and Grand Cayman are great ports. Please check out our Caribbean Port Chat section, there are tons of posts on each one.
All I can tell you is get ready to have the best vacation of your life. The service on board is absolutely amazing. Make sure you bring extra film (or memory chips), batteries, sun screen, sun glasses, and a smile. You have to try the chocolate melting cake at least one night, it is so yummy. You don't have to buy every picture the photographers take of you, but do look through them. Maybe purchase the one on formal night(s) as they really do a fantastic job with their pictures. Make sure to read the newsletter they leave in your cabin each evening, it lists all the events/times/places and specials. Your cabin key (really like a charge card) is used for all purchases on board, to get on and off the ship, and to get into your cabin, so keep it with you always. If you don't have your passport, it would be a good idea to get it. It's not necessary for getting on and off the ship, but in case something would happen, you'd need it to fly home. And, of course, after this cruise, you're going to want to do others where it might actually be required.
If there's anything specific we can help you with, please let us know and we'll try our best. Otherwise, please look around our various sections and hopefully you can find some helpful information. Best wishes!