Of all the things I've seen mentioned so far, I've taken almost all of them. but of all of them, the only ones that I've ever used were the zip lock bags, the extra folding bag to bring the extra "stuff" my wife bought and the duct tape. I actually didn't use the duct tape on the cruise. I was out of town on business a few weeks after the cruise when the zipper busted on my suitcase. The duct tape happened to still be in the front pocket.
Of course, there was that couple a few months ago who could have used that duct tape on the balcony and saved a lot of trouble.