Mrs. Pott's Cupboard (yes, it's the one in Fantasyland the PP referred to.)
Plaza Ice Cream parlor has really good coke floats.
Aloha Isle over on the way to Jungle Cruise has those yummy Dole Whip cones, twists or floats.
Oh, and also Auntie Gravity's over across from the cars has fruit smoothies and floats too.