In the past few months I’ve had to repair my iPhone, my digital camera, and my Macbook Pro. During this time I’ve found the iFixit’s magnetic mat indispensable. Not only does the magnetic surface mean fewer lost screws, but it’s whiteboard surface means I can keep track of what came from where. Intelligently, iFixit includes a very nice fine-tipped dry-erase marker from Staedtler for quickly jotting down repair notes (that also features a bit of wool on the cap for erasing them, too). The pro model mat, which I own, also features a nonslip foam backing much like that of a mousepad which when flipped upside down features cutouts that act like cups.
I like mine so much that it never leaves my desk as it serves as miniature whiteboard, mousepad, and DIY repair station.