The only way to purchase things on the ship or at Castaway Cay is with your KTTW card. However, you can go to guest services (on the ship) and have Disney Dollars applied to your account.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!