I Can't Draw on the Run

I have trouble drawing when I'm not sitting in my "drawing space." I like to sit at my desk, with my board and supplies "just so," and with low distraction for a few hours. How much time do I have to do this? Not a whole lot. My teacher encourages me to carry a sketchbook, and the books I read encourage me to carry a sketchbook. Yet I can't sketch on a bus or while I'm waiting somewhere. I am too distracted and unable to focus. I'm thinking about buying a book actually made for drawing (instead of using a lined notebook) with the thinking that maybe I can trick my brain into bringing my mental drawing space with me.