I sketch people pretty much every time I am on a train, a plane or a boat (in this case on our cruise last December). I don't use any pencil and alternate between a brush pen (refillable Copic) and a 05 Micron. It's a great way to pass the time and if you're lucky you get some nice characters for future projects.
These last 4 were done on the last night of our cruise at the "American Idol" Karaoke contest. Ted, the guy in the black turtle neck doing the air guitar, stole the show.