Portable DVD player w/ headphones. Get him use to the headphones ahead of time, and make sure the battery is charged. If you have a direct flight from Pa, the flight shouldn't be too long, and a full lengh Disney movie may be just the right thing. Or even a couple of DVDs of his favorite shows. You may have to change the movie mid way, but at least he'll have something familiar to look at. We have used small things of playdough. There are some out there that have "tools" attached (we have ones that make flowers, teddy bear forms, french fries and that kind of thing). Window clings that he can use to decorate the window, and can be removed when you get off. A couple of new toys that he can unwrap once in the air. Snacks stuff he likes to eat, including any drinks/juices. If your DS is learning letters, colors or shapes, either get, or make some flash cards with some stuff on them and play a learning game. That was a hit with us. We made a fun game of it, and DS had extra special attention, rather than being bored sitting in a big plane. You can even laminate (and double side) the cards ans put a hole in one of the corners and use a metal ring to hold them all together. That way you can pull them out while in a line if need be.
If you have a layover anywhere, bring a couple of baloons you can blow up while waiting for your connection. Find an uncrowed area where he can bat it around a bit. My DS loved that! And when it is time to get on the plane, either find another family with a little one to pass it off to, or make a small hole in it, deflate it, and put it in the trash. This allowed my DS to blow off some steam and get some activity before having to get back on another plane. Saved our sanity a bit, too!
One of the things DS loved while waiting in line was squirting us with one of those fan misters we bought at MK. He thought that was funny (of course, we exagerated a bit in our reactions to make him laugh). Also loved fanning us with the small battery operated fans. Bubbles seem best for while waiting for parades or fireworks to begin. In line they can annoy others around you, especially if they begin to pop on other people. For in line, you could get one of those kalidoscope type things. You know, one of those things with the little colored pieces inside that form different shapes when you look up at light and slowly spin it around. Also, a view master. There are so many different disks for them these days, even 3-D ones. And little carry cases to keep the disks safe. You can have him count things, or describe some of the objects (shapes, colors...) he sees. Not only would that kill some time, it is also a useful learning tool. He'll think it is a big game, only you will know differently (and the many other adults around you of course).