Try to look at the ports you'll be stopping at and go ahead and try to pick the excursions you'd like to do. At least look at them and narrow down your choices so that you'll have an idea what to pick once you get on the ship. We spend a lot of time worrying about what we were going to do, it would have been easier if we picked before we went. Looks like the only destination on your cruise that I went to was Cozumel. That's good, because it was the best stop we made. The shopping there is good, plenty of shops and the stuff is cheap. We had several that did the island tour on Cozumel, and they all enjoyed it. But if you're planning on shopping, Cozumel is a good choice. Don't know much about your other destinations.
On the ship most everything will be taken care of. More food than you can imagine, 24 hours a day. Tea and water, and some juice, (apple and fruit punch for us) is also available for free 24 hours, but everything else cost money. If you drink a lot of soft drinks then the way to go is a "drink card". You pay for the card then all the drinks afterward are free with the card. I just stuck with the free stuff.
Room service in nice, I ordered that everyday just to get a snack before going to breakfast. The fridge in your room will have a few cokes and drinks in it, but they cost money. You can have them come and take them out, then put whatever you want in the fridge. I just kept some juice and food from the buffet in the fridge for whenever I wanted a snack. Worked out pretty good.
Take a power strip or extension cord with you for sure. Something you can plug into the wall, then plug several things into it. There is usually only one outlet in the room. If you have a hair dryer, curling iron, cell phone charger, alarm clock, etc., one outlet fills up pretty quick. And it gets old plugging and unplugging stuff all the time. This was the best thing I took on the trip. Oh, yea, and if you need an alarm clock, you'd better take that too.
They have plenty of towels and stuff in the bathroom, don't bother taking anything like that. They had plenty of soap, shampoo, etc. also, so you can leave that at home if you're trying to pack light.
And pack light if you can. I took too many clothes, it's easy to do. We did the dress dinner every night, and I enjoyed it. But that was where the majority of my clothes went. It's hard to wear the same dressy clothes every night. But the rest of the time was mostly shorts and T-Shirts. There are some shows and stuff at night to go to, everyone wears whatever they want. Shorts and T-Shirts to suites, and everything in between.