I often sketch out code, short stories, or (to me) fleetingly puzzling mathematics with a notepad and pen. Try it. It's the most versatile note-taking system ever devised.

Also, it has the plus-side of being 'interesting'. People are attracted to scribbles they understand them - but crack open your laptop in a pub or cafe and people will assume that you're a rabidly, uninterruptibly busy, professional. And hell, maybe you are, but whose day isn't brightened by someone asking them what they're so engrossed in?