If you are flying within 3 hours of naptime skip having him do it and he may fall asleep on the plane. Mine always did due to the sound I think of the engine.
I would make sure you have ample snacks and fluids, change of clothes and diapers and wouldn't worry too much if he is on your lap, that in itself may tick him off however not an option for him to sit still. The portable drawing boards that they have, portable aqua doodles are good. I say he may surprise you and fall asleep if you bypass the nap before, getting him up earlier that day or are traveling close to his already nap time. Mine would fall asleep within 20 minutes of take off. My daughter was on my lap and about 17 mos old and I put her against me and she fell asleep the entire 2.5 hour flight! :) Also, let him run around when you are that gate sitting there waiting, I chased my daughter around the chairs a few times, just to burn off steam before we boarded, hee hee.
Also have a strawed drink, pacifier if he takes one or sucker handy with take off and landing to help the pressure in his ears.