I would just remember to bring extra clothes for the plane. We have done several 5+ hour plane rides with Gabe, but the turbulence got to him on the little two-hour flight to Florida last week. I'll spare you the details, but.. bring wipes and clothes in your carry-on. Lots of them. For all travelers! Just in case..
As for activities: I basically went with a bag of new tricks. I brought a new knock-knock joke book on a previous trip, which he never saw before and thought was hilarious. That was good for about 15 minutes :) I also picked up a few new travel-friendly games that he never saw before -- one was like colorforms and he enjoyed that for quite a while. We also went to a restaurant recently and they had a little etch-a-sketch, and thought that would also work really well on a plane. And.. kid earphones.
Happy travels!