The wrinkle spray I use is Downy Wrinkle Release. It works well for small wrinkles, but not so well for something that really needs to be pressed!
You can also try hanging your clothes in the bathroom with the hot water on in the shower.
I believe there are laundry rooms with irons on Carnival ships. The price for pressing a couple of things is really not that much if you don't want to fool with it yourself!
Have a wonderful wrinkle free cruise!