There are a few ways to get an appetizer included on the basic plan:
1) Le Cellier's prix fixe menu, which is permitted on the basic DDP
2) Cinderella's Royal Table, which is a fixed price meal and always includes an appetizer
3) Family style all you can eat restaurants like Ohana
4) Fantasmic Dining Package at Brown Derby or Mama Melrose
That's it. Signature restaurants do not include an appetizer on the basic, even though they cost 2 credits per person.