Foil Blankets

Foil blankets are in essence, emergency blankets. The idea is simple: the body heat that you lose is reflected by the foil. Note that, being thin, these types of blankets are not good at keeping cold out. They are made to keep heat in. If you buy foil blankets, make sure you find out exactly how to use them properly.
Foil Blankets:

Foil Blankets pictured: Emergency Mylar Blankets – 84″ x 52″ (4 Pack) by Mylar Blankets