I'm going to try to break down everything from leaving the port to coming back, and everything in between.
First things first. I'm 23 and went with 4 friends on Carnival Fascination, departed Saturday May 18th and came back Thursday morning.
LEAVING THE PORT: This was a cake walk, we parked at some parking lot at the corner before you turn down towards the port, and it was only $8 a night and the crew was super nice, had no problems there. And there were couches and snacks and what not that we were able to eat before they drove us in shuttles by customs. Once we got there it was really smooth, no problems at the bag check or anything. After we got on the ship with our carry-on bag (I packed sandals, a swim suit, sun lotion, ipod, wallet, just miscellaneous stuff that could hold me over until my luggage came, which was around 2 I'd say), we went right by the pool.