If you're on the DDP, a drink is included in a CS meal.
If you're paying out of pocket, only childrens' meals come with a drink. Adult menu items (drink, dessert, entree) are a la carte at CS places. Iced water is free, so you can always order that if you don't care to pay for a drink. (That's what I do - order iced water with my meal and save a few dollars for a snack later.)