In my classes and here on my blog I've talked and written about the importance of a pocket notebook or journal, repeatedly and often. Jane and I explored this with our "Field Experiments" posts. I find that when I carry a sketchbook/journal with me ALL the time I use it more often. Even if all i'm doing is writing down which train I need to take and when, I'm using it. Having it on me all the time lets me use it for sketching and journaling whenever I want or need.
I've taken to carrying Field Notes and a BanditApple Carnet peewee in my pocket along with a mechanical pencil and a black ink pen in my coat pocket. It's a barebones journaling set up. No color just graphite and ink.
Because I've been keeping my journal in my inside coat pocket the point of my pencil has been pocking through. I jabbed my hand with it but I was more afraid I'd break a point off or jab someone else on the train. I made myself a little pen sheath that fits over the top of my flap cover.