Most things can be. There at least used to be some kiosk type places that were cash only, unless they are all connected now too. What types of expenses are you thinking of that might not be?
Yes we were able to charge almost everything back to the room like pp stated. It has been quite some time since we have been there but I think there was a limit of either $500 or $750. After that you'd have to go pay it off to restart.
In February there were still some kiosk places that were disconnected. It is always a good idea to take a small amount of cash. However overall everything can be charged to your room. Every so often go to the desk and add cards depending on how you are spending. It helped me keep track of our costs. I tried to keep a little ahead and then on last day I only added what I knew we would spend and then used the extra giftcards in the park.