On the regular DDP you get one entree, one desert, and one fountain drink. On the deluxe DDP you get one appetizer, one entree, one dessert, and one fountain drink. The drink is usually limited to a coke product, coffee, or tea. Normally the specialty drinks do not count on the plan (there are a few exceptions, like the milk shakes at WCC).
What I was trying to say about the appetizers was that in most cases if you are on the DDP (regardless of the plan) you cannot select something from the appetizer menu and try to get that as your entree or dessert. There are a few exceptions, but in most cases they will not let you make that trade/substitution. If you are on the DxDP then you get an appetizer with each meal.