The Coke machines are few and far between, but you can't go 50 feet in the parks without tripping over a cart that sells soft drinks and bottled water (all Coke products). A 20-once bottle of Coke is $2.50 and 20-ounce bottles of water are $2.00.
Don;t worry, you won;t have any trouble finding regular Coke and diet Coke anywhere on WDW property. Caffine-free Coke, on the other hand, is nowhere to be found, and Pepsi is a four-letter word to Disney!