Welcome aboard, Suzanne! I loved exploring Europe with Disney Cruise Line a few summers ago. It was definitely the trip of a lifetime, and I'm sure you'll make some magical memories too!
The Disney Magic is
cashless, so no need to have any cash onboard. Each guest receives a Key To The World Card to use onboard. This serves as an i.d. of sorts, as well as your stateroom key, photography link for your photos taken onboard, and your chargecard for any purchases made on the ship. I love that I don't have to keep cash with me around the ship. Whenever I'd like a fruity drink or want to purchase a souvenir in the gift shops, I just hand over my Key To The World Card and the purchase is charged to my stateroom. You may want a few singles (U.S. dollars) to tip the Cast Member who delivers any room service orders you place, but other than that, no cash is necessary onboard.
My family and I do bring Disney Gift Cards that we purchase leading up to our cruise, and use those as a credit for our stateroom account. Just swing by Guest Services onboard and they can credit your account with those Gift Cards. Hold onto them until the end of the sailing though just in case you don't spend all the credit, and they'll put the remaining balance back on the card.
Even
Port Adventures are charged to your stateroom account onboard, so no need to pay for them ahead of time or while onboard. Those charges will show up at the end of your sailing when you receive your stateroom account list of charges. If you'd like to check it throughout the sailing, the Cast Members at Guest Services are happy to print the account for you as of that day.
Have fun as you embark on this magical adventure overseas, Suzanne! Stop back if we can help with any other questions before you set sail!
Marcy