Admittedly I haven't done this yet, but I saw it in the campgrounds last year and thought it was genius after some rough mornings.

Here's a little guide that shows how to set it up

And here is a nice quality space blanket. From what I can tell these might have a little more of a matte finish so that you aren't creating a mirror that hits people in the face. The cheaper types that you can get for a couple bucks apparently flap like a potato chip bag in the wind, and are more mirror-like.