One of the more useful tools I’ve picked up along the way is a 98 inch aluminum cutting guide.  I originally picked it up for it’s intended purpose, as a guide for a circular saw to ensure you get a straight edge on longer cuts.  It’s also extremely handy, however, for laying out longer track center lines ( in a yard for instance).  It breaks down into two halves for easy storage.  Most hardware chains care it.  The Home Depot version can be found here.