Are there still movies on longer flights? If so, you'll have that.
Hubby's parents bought them little magnetic games, like scrabble, connect 4, etc, when they were on flights from Seattle to various Asian countries when they were kids.
You could look into extra batteries for the PSP and DVD players. Hubby says (though hubby's info might be outdated) longer flight planes might even have charger areas. (I personally raised my eyebrow at that)
Hubby's parents also had them bring books. If there is the "next Harry Potter" series out while flying, some copies of those books could take a whole flight.
Hubby also says to make sure the kids get up and walk around the cabin every so often, b/c that long sitting on your behind is difficult.
Lastly, hubby's mom, he says, didn't care how late they stayed up the night before the flight, so that they would be tired (I will mention that being crabby in their family was absolutely NOT allowed, with painful punishments for crabbiness enforced, so in a non-painful-punishment household, I'm not sure how this sort of thing could be enforced, so lots of talking might have to be done to let them know they might be tired and crabby but can sleep on the plane), and then she made them as comfy as possible on the plane so they could fall asleep.
Hubby is the middle of 3, with about 10 years from oldest to youngest.