+1 on the Thermolite bivy, Heatsheet, wool blanket and Sportsman's blankets. I keep a bedroll of a wool blanket and sportsman's blanket in the truck year round, along with a blue foam ground pad.

I stopped carrying mylar sheets several years ago for several reasons, although I am using one to cover a set of windows this winter. *laughs* The fool things are better than nothing, particularly if used right, but their limits are pretty broad.