Small or lightweight items are best for travel. When I went to TX to visit family recently, I took a half skein of variegated to make a pidge and a full skein of ecru to make a scarf in Feather and Fan stitch.
I also did a shawl recently in Feather and Fan with that white baby yard that has a thread of floss incorporated for sparkle...it was a fairly light project to carry and bunched up nice and small to fit in a big purse thanks to the lace stitch.
(Note: I do NOT knit while riding in a moving car, nor do I recommend it to anyone else--if a deer or dog ran out in front of the car, or some idiot pulled out without looking, the needle could wind up impaling someone.)