facing this dilemma myself back in may, i chose to cast on a simple lace scarf project with some laceweight yarn on a pair of pencils. put some cap erasers on the ends, and the stitches won't fall off. i chose a really nice gray black variegated yarn, so as not to worry about the graphite marking up my yarn. it's working out very nicely! i put the project in a pencil bag, and now i pull it out whenever i'm in line at the grocery store or the bank, since i didn't finish it on the plane.
once you get past the security knuckleheads, you have to face those flight attendants who are morons. (i'm positive all the security folks are knuckleheads, but many flight attendants aren't morons, and knit themselves.) they may tell you to put your work away inflight "because you could stab yourself during turbulence." and THAT'S the reason for the pencils. i'd've acquiesced quietly had i gotten that request, as long as every other person on the plane ALSO had to put their writing implements away.
flying nowadays is inhuman. knitting distracts from your realization of this. good luck.