I might be a little biased because I really did not enjoy my cruise but...
When you go to board your cruise they will ask for a credit and give you a "fun Card, "Ship Card" etc. From experiance there is a much different feeling using your fun card to pay for a round of shots than it is using YOUR credit card. Becareful cause the drinks charges get racked up fast. I was on a 4 day cruise and my bill at the end that they nicely slid under my door while sleeping off said drinks was 900-1000 dollars.
Your first hour or so of your trip you will sit down with an orange dingy around your neck as they explain to you that if the ship goes down this thing will probably not save your life. (Sarcastic!) It does take awhile though.
Take advantage of the day trips they are expensive and if your adventerous you can get them for cheaper when you dock at a location.
Like I mentioned I didnt like being told to be back at the ship at this time or if I brought alchol back to the ship they would "store" it for me (See Fun Card charges above) I almost always go on all inclusive vacations but decided to switch it up a bit, I think Ill stay with my all inclusives.