Whenever I do a complete strip down a playfield, I pick up a package of small 3"-4" zip-lok type bags. I usually get them in various sizes from McMaster Carr while I'm ordering other stuff, but think you can get them for a couple bucks in the craft area of Walmart. When taking something off the playfield, group the associated screws, nuts, posts, etc for that piece into one bag and write some description on it reminding you where it came from. Number these bags as you go along.
I keep a notebook with me and track the sequence of my teardown. I list the associated baggie # and add little notes along the way (anything that might make orientation clearer, if something has to be slid in/out a certain way, etc.). This, as well as more pictures as things come out, should make things pretty easy going back together with (hopefully) no leftover parts.