Do you put a certain amount on your room key each day? Or is there no limit and you pay at the end of your stay?
When you check in, they'll ask if you want to set up a room charge. It can be backed up with credit card, debit card (with VISA/MC logo), travelers checks, cash or even Disney Dollars. Each level of resort has a maximum room charge amount (you can set it up to that limit, it doesn't have to be AT that limit): $500 for Values, $1,000 for Moderates, $1,500 for Deluxes.
If you use a credit or debit card, there is NO HOLD placed on your account. They will "run" the card just to make sure it's on an active account, but there is NO HOLD.
When you reach your limit or you check out or check out time occurs, whichever comes first, your card will be charged the amount you charged on the room account.
Let's say you set up a $500 room charge and have a current balance of $490. You try to room charge a $15 item. The charge will be declined. Your card will be charged the amount of your balance ($490). They have it set up that you can call your resort's front desk and instantly set up another room charge. That will be done in seconds, and you can go charge that $15 item now.
You can get printouts of your room charge account from the front desk as often as you'd like.
I strongly prefer using the room charge because of its incredible convenience. I don't have to carry cash or a credit/debit card with me. At the end of vacation, my account has only one or two large charges rather than 57 individual purchases to try to track.