I got a Roswell Park handy dandy reusable score card. It rocks.
I don't know how you "in your head" guys do it, and I wonder how accurate you are.
I'm a in your head guy, and it's easy to do for me at Rankin, or someplace I've played a few times, but at a course I've never played before, it's tough. I can always remember my overall score, and if I can't remember every hole I just put in an overall score in my scorebook here. The scorebook rocks by the way. I think it's the most under utilized features of this great website.