S.B.
Dum Dums are a great idea!! I'll be bringing those when we go on our trip to CA!! Also, books are good if he likes to read. I second the magnadoodle and color wonder idea. Anything that is new, or that he hasn't seen in a while is good, too! IT will capture his attention longer. And, bring all kinds of snacks! Goldfish are great, fruit snacks, granola bars, and whatever his favorite snack is, bring it! I don't know what the new rules are about bringing drinks in...but if you can, bring or buy plenty of water. They ran out of bottled water the last time we flew...and whatever you do, DON'T drink the tap water! There have been all kinds of reports about the gross stuff in the tap water on planes.
If you have a portable DVD player, bring that. We don't have one, but there was a girl on our last trip that did, and she was completely satisfied watching her movie. I always buy a "special" toy that is new just for a plane trip. I don't spend a lot of money on it, but its new and it works for my girls...at least for a while!
Good luck and have fun! Where in CA are you going?
=) S.