I carry a sketch book with me at all times, and draw when I have to wait for someone or something. It relieves both stress and boredom.
I also draw to document my travels much in the same way others take photographs. Drawing forces me to look closely and really see what I'm looking at. I have been drawing on full sheet watercolor paper, which is very liberating from the small scale sketchbooks I carry. I love the feel of the pencil on handmade watercolor paper.
I also tend to see drawing as an artistic exercise that maintains good hand-eye coordination.