I agree with everyone else, I travel with my wife and two daughters. We normally have four large suitcases and a couple of carry on's. We always manage to be able to unpack everything between the closet and the drawers (which are everywhere) The suitcases (soft sided but not collapsable) under the bed (we do sack them inside each other though). As we go through our clothes, we then put the dirty things in the suitcases to get them out of the way. You can have a fairly tidy cabin doing this.
If you already have luggage and it can store inside of each other, you should not have to go out an buy special stuff. There is room under the beds for at least four large suitcases worth of area.
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