Snack Cart
I let my kids pick a snack from the snack cart. This always keeps them busy for awhile.
First there is the time it takes for them to decide what they want, they the anticipation as they wait for the cart to arrive at their seat. Then the joy when they receive their goods.
And if you don't give your kids, chips etc all that often it is a real treat.
It might cost you a bit of money, as opposed to packing your own snacks, but there is the novalty factor. And the kids are on holiday too.
This is now part and parcel of going on an aeroplane for my family and also acts as a great bribe to keep them well behaved at the airport prior.