Games that use a pen or pencil are perfect to play on airplanes, since you can lean on the tray top. The following ideas are especially enjoyed by players who are sitting in a row. Unlike backseat games, which can get fairly boisterous, these airplane pastimes are a bit quieter, so you won't make enemies of your fellow fliers.
Create strange-looking people, beasts, or any combination of both by folding a piece of paper into three equal sections. One person draws the face in the top section, then folds down the paper so the next person can't see it. That person then draws the midsection of the body, folds down the paper, and passes it to the third person, who sketches the legs in the bottom section. Finally, unfold the paper and name your creature.
This is a good game for people sitting in a row. Player 1, on one end, thinks of a word. Player 2, next to 1, closes his or her eyes and holds out an arm. Using a finger, Player 1 "writes" the word on Player 2's arm. The word gets passed down the row — and maybe across the aisle — until it reaches the last person in your party. That person says the word he thinks was written on his arm out loud, and Player 1 says the original word. Let Player 2 start the next round, and so on.
You end up with a lot of idle time when you travel by air. Scavenger hunts are an easy way to spend those hours calmly.