I actually brought a PB&J (made back at the resort) into a TS restaurant more than once. I buy her a drink and dessert and don't worry about it. If they don't have anything for my DD to eat, then what I am supposed to do? I let the server know and make sure I tip well. She also sometimes eats PB&Js when we eat at counter service restaurants. For instance, we LOVE Flame Tree BBQ, but there is no vegetarian meal option there for kids on the DDP.
Honestly, this is the only way my son can survive a trip to pretty much anywhere! I buy a loaf of bread and a jar of PB and we make a sandwich anywhere he can't get grilled cheese. As I mentioned above, he has Asperger's and one way it manifests is in food texture aversions. The kid won't eat chicken fingers, mac & cheese (he used to, but regressed), hot dogs or pizza. That rules out 95% of all kids food options at WDW! Like you, we always tip well and I figure they'd rather have DH and I spending our money on good restaurants while DS eats his sandwich.
