fruit, veggies, animal crackers, cold cuts, cheese cut up, and lotsa water bottles (freeze some full, freeze some half full and add water, and just chill some... that way you'll have nice cold water from beginning to end, and the frozen ones will keep everything in the cooler cold!)
cereal necklaces... on our first airplane trip w/kids, i brought dd shoestring licorice and fruit loops to make necklaces... she gave them out to the flight attendants... they had the stickiest necks in the business, i am sure... but they thanked her over the p.a. system and it was priceless!