On our last trip, I went to the grocery store and picked out selections of our favorites as well as a few special options. We went for density over air filled packages for the most part, but I made our kid little snack bags that went with the park we were going to: international treats for Epcot, Star Wars themed for Hollywood Studios, Lion King and trail foods for Animal Kingdom. I did not theme one for Magic Kingdom - I promised a giant Mickey cookie instead. LOL
For the hotel room I picked up breakfast bars, some mini-cans of Pringles, some snack mixes.