I am definately an over-packer and always have clothes we don't even wear. But it isn't as much the clothes as the "stuff" you feel you must have, and can't buy on the ship. I would have a made a great girl-scout since I pack to be prepared for anything!
However, the best idea I have come up with for packing and keeping my suitcase organized is to use zip-lock bags. Not only do I use the gallon size, I buy the x-large and jumbo bags at Dollar Tree. I lay out a stack of T-shirts, or shorts, or even slacks, then fold the stack together and slip it into one of these bags and stack them in my suitcase. They work great and the clothes are not wrinkled. They are great for damp or soiled items going back into the suitcase for the return trip as well.