For my very first cruise, 12 years ago, I bought a classic long, straight black skirt --- and by pure luck discovered that it won't wrinkle no matter how I pack it or how long I sit in it. Once it even got the better part of someone's pina colada spilled on it, and after blotting up the mess it showed no sign of the accident. Needless to say, I would never think of cruising without it!
I have an assortment of tops to go with it: black beaded, gold spangled, blue sparkly, cream lace, and green lace. I get complements on all of the combinations, and people never seem to notice I'm wearing the same skirt all the time.