We spent a day off property last trip, though we did return for a late dinner at WCC. But we somehow managed to use up all our credits. Just stay on top of them, and let those boys eat whatever snacks their hearts (or stomachs) desire, because those snack credits don't go as fast as you think they will.
Some have reported using CS credits to get "grab and go" meals at their resort shops. These apparently are premade sandwiches and sides that you could take with you to IOA. I know that's not everybody's style, but most hungry, teenage boys will eat almost anything, and it might help cut your offsite food bill. You could also get breakfast sandwiches and juice to take with you in the car to eat while driving to IOA.
For TS, I'd probably try one 2 credit restaurant and add an extra breakfast to another day. A TS breakfast + a TS dinner is a lot, but I'm sure somehow the boys could manage. If it's too much for you and your dh, you could split either the breakfast or dinner (as long as it's not a buffet), but then you'd have more of those pesky extra credits.