For CS, I would suggest Stage Door at Disneyland (or Golden Horseshoe if it's raining or you need some air conditioning) and Corn Dog Castle in DCA.
For sit down, I love the Plaza at Disneyland. We often get the Chicken Alfredo Penne for lunch and it keeps us so full that we can just have something light for dinner like a churro.
Also, for a free snack don't miss the Mission Tortilla Factory. It's a warm, happy, little present. It always makes me happy.