What to pack? Suggestions on items to bring.?

We did the very same itinerary two years ago with Royal Caribbean. It will be very hot and humid, so pack shorts, tank tops, and the like. Also, if you are going on excursions, remember to pack comfortable shoes. 100% cotton is always best, but if not, make sure your clothes contain as much cotton as possible. Senthetic material will stick to your skin and make you miserable. Make sure you have at least two bathing suits, so you will always have a dry one. We cruise every year, but we have never gone with Carnival, but I think they are all pretty much the same, so there will probably be one formal night on your trip. A tail dress is fine, and a tux is really not necessary, a nice suit will do. Other nights will probably be just as if you were going to a restaurant at home (not dressy). On Royal Caribbean there are no jeans or shorts allowed in the dining room, but slacks and casual shirts okay, and sun dresses, or nice capris and tops okay.Also, years ago crusing was much more formal, everyone is more relaxed these days. I hope you will enjoy cozumel as much as we did. Just remember, pack as lightly as possible. I have a tendency to pack too many shoes, I am still trying to cut back. Have a great time. Also, don't forget your camera and sun hats or caps.