One piece of stationary which I love (I bought 500 of them when I found them) and have never found again, which REALLY helps, they are a regular plastic sheet with another stuck to the end, so you end up with one that folds in again (Basicaly A3 in size).
Each of my books has one with the stage (and all abbreviations) on it in the outer pocket at the back. As I write my stage directions on paper, I also draw the paths etc on an overhead transparancy, which I put in the right pocket as well, giving me an overlay. As it changes I just erase the overhead, and if need be, at a later date I photocopy the transparancys with the stage layout behind it.