Because airplane seats are so close together that you can't pick things up off the floor

These markers are brilliant -- the caps stay attached, so there's no chasing them down when you're traveling. And they're six to a pack, an ideal number for a trip. Oh, and washable of course! They're definitely more expensive, but worth it to have a pack or two around, I think.

They're Crayola Flip-Top Markers, and I bought them at TRU.