Keep an eye on your pants.
I will second what GD said about dressing for dinner. Susan took it as an opportunity to get dressed up which she normally doesn't get to do too much and I was comfortable with a dress shirt, slacks and a sports coat (no tie). Although I did wear a suit for the "formal" night.
If you want to go hog-wild, you can rent a tux on board - I can't remember if they had formal gown rentals or not, but I believe they did.