We use our credit cards (mostly for the airmiles) for nearly everything on vacation -- but especially hotel, and car rental (if we rent).
The reason is that if there is a problem with your room (or car) and the problem is not resolved to your satisfaction, you can instruct the CC company to withhold payment and dispute the charges. Virtually every time you will end up not having to pay for unsatisfactory service. The CC company will stick up for *you*.
We take only minimal cash, and when we do need more we use the ATM, or try to get it as "cash back" after a purchase at the grocery store. We have always figured the $2-3 charge from the ATM is better than potentially losing hundreds of dollars.
But honestly, you can use your CC almost everywhere.
Also, isn't there a bank in WDW that will cash a check? I think there used to be. That's another option, that might avoid ATM fees.
April