I carry an Adventure Medical Kits survival blanket in my PSK.
My reasoning is that some form of rapid shelter is the second most important thing you can carry besides fire starting equipment, especially here in Montana. In 4 years of being a member of SAR I have seen people die from hypothermia that shouldn't have.
Remember your rule of 3's
3 minutes w/o air
3 hours w/o warmth
3 days w/o water
3 weeks w/o food