Hi Kari,
Yes, you can use your room key (Key To The World card) to purchase food and merchandise at many locations throughout Walt Disney World. All you need to do is register a credit card against your reservation when you complete on-line check-in or when you check-in at Disney's Pop Century Resort.
At the end of your stay, you will receive a list of all purchases charged to your card during your visit and the total amount spent will then be charged to your credit card.
It is worth noting that you can set up a charge spending limit (which you can increase
or decrease if necessary) and can also give charging privileges
selectively to individual members of your party.
My family always find this to be the easiest and most convenient way to pay for our purchases.
Disney Dollars are the official currency of Walt Disney World. They can be purchased in denominations of $1, $5 and $10 - each with its own Disney Character portrait. You can find out more about Disney Dollars including where they can be purchased and used
HERE.
Wishing you a magical trip!