My rule of packing is to put everything you think you should take for the cruise on the bed. Then pack the formal wear, the swimsuit, the bathroom items and a pair of sandals (or flip flops). Then take about half of what is left because you will not wear it and you will end up with new clothing (t-shirts, shorts hats etc...) in the first port you hit anyway.
Dave is correct about the sweater or light jacket. My wife is always cold in the ship, so she likes to have a sweater for when we go to the theater or lounges...
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007