After years of rigorous back-seat research, I can report that the perfect travel snack must pass three tests: no melt, no crumble, no negotiation.
The podium
Gold goes to breadsticks, which are indestructible. Silver to apple slices in a cold tin. Bronze to the humble box of raisins, docked points for the eventual discovery of raisins in the seat rails, the door pocket, and one shoe.
Bananas are banned. You know why.