Actually, you can make payments on a room-only reservation. As a matter of fact you can even pay more than what is owed, the Disney representative will escrow your funds into a reserve funds section under your reservation which can be used towards ticket purchases, dining, etc. or you can have the funds refunded to the credit card that was used to place the reservation upon completion of your stay. I have been using this tactic for the past three years and everything works out perfectly when I arrive to check-in. There is no need to worry about maxing out the credit/debit cards and the reserve funds will be there at your disposal. You cannot use this method on Disney packages, Disney will not allow it.