I have a good friend who used to be a Lead at Rancho and according to him all Buffeteria-Style food locations (ie. Rancho, Pizza Port, Plaza Inn, French Market, etc.) at the resort alow free fountain drink refills. Although there is no specific signage, he used to go through the dining area making sure guests knew of this policy.
As far as coffee goes, I have heard that you can purchase a mug at the Market House on Main Street and it is refillable for the duration of your stay, but I am not sure about this as I don't drink coffee.