1. Large mouth gatoraid bottle. Easier to.. um.. refill (pee bottle)
2. Large Sub Sandwich. Skip the foods that will give you the runs.
3. NO COFFEE!! Water, juices, etc. (cooler if you have room)
4. Apples bananas grapes (cold grapes rock enroute)
5. Also try a Camel Pak back pack. Strap it on the seat.
6. Bagel with peanut butter.

Just a few.

(Not that I've spent 8 hours a day in a plane during the summer or anything)