I keep a small moleskine for medium to large notes. I keep small sheets of paper in my back pocket at all time to jot down something to do later today or tomorrow and cross out when done.
I also catch myself implementing some GTD tips.
I also catch myself implementing some GTD tips.
Still, I don't think I'd buy them again. Seconding Yan's sentiment, a notecard (or napkin!) is all you need in moments of inspiration.