Onboard purchases are paid for using your cruise card, which doubles as your room key. This card is set up before boarding (you can provide the card details at the time of online check-in) and serves as your ID to get on and off the ship, providing you access to your cabin. You can either link it to a debit or credit account or sometimes provide cash upfront to fund your onboard spending. Guests are charged from the Onboard Expense account. The currency sometimes may depend on the itinerary.