Tons of good spots. We bring all of our own food in. You can eat inside at most QS places. If it's a "busy" season, we'll eat at slightly off peak hours so that we're not taking up tables that paying customers would need. However, during summer that's almost never an issue, even at peak lunch. Here are a few of the places we use...
MK - Tomorrowland Terrace (when it's open), Cosmic Rays, Pecos Bill, Pinocchio. If the weather is nice, we'll use the tables that are right across from Pirates entrance, or in that general area.
Epcot - Electric Umbrella, or inside The Land building. If it's nice out, we'll sit at the outside tables of Electric Umbrella (DW gets cold inside there)
AK - The restaurant across from Dinosaur, forget its' name. Either inside or out, depending on weather. The pizza place, again forget the name.
HS - If it's nice, we'll use the tables near the boat/dinosaur, or the tables on Sunset Blvd. Sometimes we use the Commissary, or the pizza place near Muppets if the weather is hot/cold/raining.