Disney Dollars can be used almost everywhere at WDW.
They can be used at any shop, restaurant (table service or counter service), or vending cart in the parks, all of the Disney-owned places at Downtown Disney (and even a few of the non-Disney places), and at any of the shops, restauraunts, and food courts in the Disney resorts (not the Downtown Disney resorts or Swan and Dolphin because they are not owned by Disney). You can even use DD$ to pay your balance at Wilderness Lodge, or put money down in DD$ to activate charging on your room keys.
I recommend putting some money down when you check in to activate the charging priviledge on your room key. You can do this with cash, Disney Dollars, or debit or credit card. You select your charging limit, up to $1500 at the Wilderness Lodge and other Disney Deluxe resorts, and use your room key to pay for anything in the parks that you want.
Almost every place in the parks and Downtown Disney take room keys as well, so you will only have to carry a few bucks in cash at any given time.
I haven't stayed at WL, but the safes in the Values and Moderates have metal keys, not codes.
