Yes, ziplocs!
OP, I have no other advice but I totally empathize. I have been mourning my middle DS turning 10 (many, many health challenges, eats very little, BMI less than 13) because that means we will never do the deluxe dining plan at WDW again (which we LOVE) and now we are expected to pay $60+ for him at BB for the FDP...it is what it is and I have been mentally preparing to emphasize that we make the most of these special experiences which will be fewer in number and, so, hopefully, treasured that much more, KWIM?
His older brother will happily eat his leftovers...possibly before we even get a chance to take them out of the restaurant, LOL.