Since most cruise lines do not allow irons, here is a trick to getting wrinkles out of clothes that I learned from my dad.
If you unpack your clothes, hang them on the back of the bathroom door, (for shirts, hang them with the back of the shirt facing you if you are facing the bathroom door) and turn the shower on hot. The steam should take the wrinkles out within a reasonable amount of time.
My dad travels extensively on business, and does this all the time.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)