Disney Dollars cannot be used on the cruise in the shops because everything is charged to your room on your Key to the World card. I would suggest putting the Disney Dollars on your account earlier rather than waiting till the end of your cruise. Every time your account reaches a certain amount (not sure what amount is) they charge your credit card. I had 300.00 in Disney Dollars when we cruised in January and put this on my account before they charged my credit card. If you do not do this, and they have already charged your credit card, they will give you a credit on your credit card - it can be done but it is easier to take card of before hand. Also, as an FYI - you cannot use a Disney Gift Card at all. You also cannot use a Disney Gift Card in Downtown Disney.
Have a great cruise.
Linda