A few options depending on your needs and where you are staying.
1) stop by white water snacks at the grand. Good food, ok prices and pretty quick.
2) LaBrea bakery in downtown disney- walk up counter, not sit down service.
3) Jazz kitchen walk up window- but it doesnt open until about 8, so might not work
4) grab a quick snack in your room (pack some instant oatmeal, cereal bars- get yogurt if you have a car- you get the idea). Then after a couple hours of EE, when the park is getting busy, go to either Carnation cafe or Riverbell terrace for breakfast. You can make PS for Carnation. Or make a PS and go to Mnnies at the plaza for breakfast.