When we went in May, in my carryon, I brought things like cheese crackers, pretzels, gum, lollipops, goldfish, etc. Things that were not perishable and weren't messy on the plane. I brought our empty Bobble filter bottles and filled them once we were thru bag check.
**There is NO GUM sold in all of Disney in order to keep gum mess out of the parks. I chew gum daily to help keep my appetite down. If you are a gum chewer, remember to pack it - and of course, dispose of it properly.
In our checked bags I packed:
cereal
breakfast bars
Pirate Booty
mini bagels
&
park snack bags for each day:
7 large ziplock bags filled w/enough snacks for the kids for each day in the park w/things like goldfish, gummies, pb crackers, dried fruit, cereal bars, lollipops, etc. These were labeled with the date. Each morning, I tossed one in our stroller, and we were set to go.
The space that these items took up in the checked bags were used for souvenirs on the way home.