Just got my first AMK Heatsheet...haven't opened it yet to check it out (wanted to do a little scoping out before I fill all my kits with them.) and I got an AMK Emergency Sleeping Bag...looks about the same size as the Heatsheet, but all mylar, no orange poly-whatever. Then I got to thinking about the AMK Emergency Bivy, which is the same price as 6 or 7 Heatsheets.

Has anyone here used the Emergency Sleeping Bag, or Bivy, and would they be good things to have in my kits? From forum reviews here, I'm sure I'll be adding more Heatsheets to my kits, but are the sleeping bag and bivy necessary as well?