Whenever we go to Disney, and we fly every time, I literally have a carry-on bag dedicated to snacks & our Bobbles (a water bottle with a built-in filter in the mouthpiece). Since there are 4 of us with paid seats, each one of us gets a carry-on, plus one personal bag....SOOO, having one of the carry-ons specifically for snacks is no problem. I do not pack the snacks in the boxes they came in; everything gets emptied out into 1 or 2 grocery bags and then shoved into a mini-Mickey duffle bag. Bonus, we use the "snack bag" as our souvenir bag for the return home.
In the other carry-ons: 1 diaper bag (with a change of clothes for our DD's), 1 children's activity bag (which oldest DD rolls around), and 1 camera bag (if I can, I'll fit it in with the snack bag). No matter what time of the year it is, I always pack a lightweight jacket or pullover for the plane ride; I can fit these items in the diaper bag.
My trip isn't for another 77 days, but mentally, I am already packing