I have never sailed with Carnival, but I have cruised twice with Royal Caribbean, and loved it.
The only port in common with your itinerary is St. Thomas, which is absofuckinglutely beautiful!. We did an excursion, but we also walked around the town near the dock a little, and just didn’t want to leave! I highly HIGHLY HIGHLY recommend the Turtle Cove snorkeling tour, especially if you can get on board the Doubloon (the pirate ship, rather than the catamarans). The excursion company is www.doubloon.com and the guys that sail that ship are totally insane and a lot of fun. They keep you filled with fruit punch on the way out to the turtle island, and filled with rum with a bit of punch mixed in on the way back. They give you fake tattoos in inappropriate places (boobs for the girls, top of the head for the bald guys, the odd forehead and one buttcheek!) and sell some pretty cool t-shirts, complete with fashion show if “Brittney” (aka Chris) is on board. Oh, and the turtles are nice too!
If Carnivals’ private island is anything like RC’s Labadee or Coco Cay, then there isn’t much to do there other than soak in some sun. There probably is some snorkeling, kayaking and other “beachy” stuff, as well as a market place, but there aren’t any towns or anything like that to see or do.
One more thing about St Thomas… since it’s part of the US Virgin Islands, you have to go through US customs to get onto the island. Again, I don’t know if Carnival does things the same way (I suspect they might though) but RC takes your passport when you board so they can clear you through customs in the various ports, but the US insists that each and every damn passenger carry their own, so the ship must give them back to you by having you pick them up in the dining room on the morning of your visit to St Thomas. There were 3200 passengers on my last cruise… it took FOREVER! Seeing as you are American, you are even more screwed, because the majority of passengers are from the US, so the lines are REALLY REALLY LONG! It took some people over 2 hours to get them. Either get up very very early, or go late, because it sucks to have to wait! As a Canadian, though… well, it took us 10 minutes! It was even faster than the other non-Americans… Canadians got their own line and customs officials barely looked at the passports.
You will be given a key card, which will unlock the door to your room and serve as your method of payment and identification on board the ship. It will be linked to a credit card of yours, so don’t lose it.
We booked a balcony both times… we would never do otherwise! Especially if you can book the ones that are on the corners, aft. Well, on the RC Voyager class ships anyways… HUGE balconies!
Take the time the first day to get settled into your room, then go pass muster for the safety drill, and then explore the ship! Ask a million questions, take every passage way and staircase that isn’t marked employees only, and figure out what is where. You don’t want to be three days into your cruise and not know where things are or how things work! These ships are HUGE and there is a lot to see, and it is easy to get turned around in them.
We ended up sailing twice on the same ship (due to costs the second time, it wasn’t something we set out to do) and the second time around was so much more fun because we got into it right away. You will be hooked, no doubt about it!
Buy the motion sickness meds if you think you might need them… when the seas are calm, you do feel a slight sway back and forth, but I found it very soothing (i’m an insomniac… I have never slept as well as I did on a cruise ship!) Our last day of our second cruise was very rocky, and we had trouble walking in a straight line down hallways, but I had no problems with it… I actually really liked it! These ships are big, but not big enough to not be affected by the waves!
I hope you enjoy your cruise!