Your sail and sign card will be used for everything from your room key, to the way you get off and back on the ship, to what you pruchase on the ship. When you purchase drinks, something in the gift shop, pictures, etc. it will be applied to your sail and sign card. You can even use it in the casino, although cash is accepted their. We do not bring a lot of cash for this very reason, it's just not needed on the ship. You have the option of using a credit card, debit card, or cash (see frequently asked questions on carnivals website) to secure your sail and sign account. Also, if you do not prepay your tips, they will be applied to your sail and sign card as well ($10 / per person). Tips can be increased or decreased although I do not reccomend decreasing them as this is how the staff makes the majority of their money and they work very hard for it. Happy cruising!!!