I just got back from RCI/Vison of the Seas and I was worried about wrinkles and the iron issue. I bought Downy Wrinkle release and tried it out for weeks beforehand, and was pleased with the results on T-shirts and khakis and such, so we took that along. I also took a portable steamer. Guess what? I ever used either of them! And I am pretty picky about appearance, but guess what else? I never noticed anyone else being wrinkly either, and I am sure that not everyone is as picky as me. This tells me that people REALLY don't care -- everyone is having a great time and not really paying attnetion to stuff like wrinkles. If I didn't notice, I promise others won't either. We were careful with packing, used the dry cleaning bags for suits and dresses (they worked great) and also packed t-shirts, pants, etc, in the suitcase using the method of layering unfolded clothing into the suitcase but leaving the edges hanging out, then putting shoes and underwear in the center and folding all the hanging-out stuff up and over the bundle. Don't stress about it and have a great time!
PS Clothes irons are very different from hair irons; in hair irons the hot part can't lay flat onto any surface, and really never touch any surface at all. An iron left on could tip and lay flat on carpet or bedding, whereas a hair straightener's hot surfaces don't touch even the counter they are sitting on. Make sense?