Lots of snacks are very helpful on long trips, portable DVD player if you can buy/borrow one (or if you have a laptop with a DVD player that will work too, that's what we plan to do the next time we fly). Some comforting toys, some new toys. We also have a portable magna-doodle which worked quite well. Will he have his own seat or will he be on your lap? I found we did a bit better with dd having her own seat as she was then strapped into her car seat and didn't think she could get up and run around as easily. If there are empty seats on the plane, the airline will usually let you have them if you are traveling with a child (I guess they figure it's easiest for everyone that way).