You may bring your travel iron or steamer. It's preferred you bring one of those tiny portable ironing boards with because there's really no place to iron in the cabin.
There's also a dry-cleaner service aboard and they will do ironing also for a charge.
Many times after unpacking, I have given some of my hopelessly-wrinkled duds to my room steward to take down to the cleaners for ironing. Ironing alone is not that expensive. The charge gets put on your running tab.
If you do this immediately upon unpacking, you'll usually find your fresh and crispy clothes hanging in your closet when you return late at night from the casino, hah! I give the room steward a buck for his service.
Bahama Mama