Cruises are so much fun...don't worry. Bring an underwater camera and don't forget lots of sunscreen. I've never been on Carnival but there's always a lot to do on the ships. Bring a formal dress for the Captain's dinner and thats all ya need; maybe a nice skirt or 2 for dinner on the other nights.
About the plane......bring gum for you ears on take off and landing and you'll be fine.
Hope this helped!
If you have any questions IM me at rciprincess214