I carry the AMK Heatsheet and Tacoma Storm Shelter in my day pack as well. I have them vacuumed packed to reduce their size even more and to keep them flat. Plus the vacuum bags can make emergency water containers / collection devices if I need it.

I throw in an emergency rain poncho, just in case. Since the form factor is so small, I'm sure that I can find a use for it.

Of course I carry a modified PSP from Doug and a personal FAK.

I use to carry one of those typical space blankets, but after really reading up and understanding them, I realized they wouldn't be too useful and switched to the Heatsheet.

Obviously there are a lot of other misc. things I carry such as food and water, but I believe the point here was shelter / warmth.

I figure, for a survival situation, I could set up the shelter and snuggle in the heatsheet. Obviously, if I'm going to be in the woods for an overnighter, I have my tent and a lot of other gear with me.