A few items I suggest besides clothing:
1. My ship (RCL Radiance of the Seas) was terrific...but there was no clock in the room~so bring a travel clock
2. Extension cord with a power strip, in case there aren't enough outlets inthe cabin ~We were constantly re-charging digital camera batteries, laptop computer, and telephones (I have some techno-geeks in my family that cannot take a vacation without all of their "stuff")
3.Although we didn't have them,...I saw walkie-talkies to find other members of your family on the ship. They are helpful in the ports as well (up to 2 miles, I think).
4.If you have a choice indigital cameras, use the kind that have re-chargeable batteries. We took hundreds of pictures...my son's camera went through about 10 sets of AA batteries. I just re-charged minevery night.
5.Again, regarding cameras...everywhere you turn in a fantastic picture, with no camera skills necessary. so the optimum is a digital camera with LOTS of memory. Otherwise LOTS of film! Betwen my son and I, we took over 800 digital pictures in a week and hardly any were bad enough to be deleted.
6.Sunscreen..I never thought I would need it in Alaska...but I did, and then had to spend way too much for it on the ship.
I traveled with my 14 year old daughter and my 20 year old son. They had a blast...you will too! Its a trip of a lifetime so enjoy !