Another thing to pack in the present bag is a plastic garbage bag. Don't count on the airline or train service to have snacks that your child will like. Most airlines will allow you to order a special meal for your child. I did this the last time we flew and it was a life saver. I had a choice of a hotdog, hamburger, chicken or peanut butter and jelly.
Snacks are a big help when trying to pass the time.
Use the small plastic snack bags. Make it small so that your child will want more in a little while. Something that has worked very well for us in the car on long trips is books on tape and a cassette recorder with head phones. It's nice if you have a friend with kids around the same age that you can swap these back and forth with. We have also made some of our own books on tape with special guest readers like Grandma or Grandpa.