Let see, I have two sets of keys on a small D-ring.

On #1: my car key with a photon light, that I used on a mine tour this weekend.

On #2: my office key ring, I have a LM micra that I used the scissors this morning.

So I suppose, I go betw. a light & a knife as the most likely item I would have on me in an emergency, (excluding the the EDC that is within 3' of me 95% of the day)

But I think back to the book that have given more than any other (for a variety of reasons) to friends. A book I quoted to a group of employees doing a Grand Canyon hike next month, Cody Lundins, 98.6 degrees: the art of keeping your ass alive. I said, "Regulate your body heat. Layer for the rim, be able to strip down in the inner gorge."

Keeping with: your stranded or stuck with one item only, it doesn't preclude you being able to move around to find water or shelter or a sharp object for cutting. Keeping your body temperature in the right area is what is going to keep you alive.

So in the end I suppose I need to put my Light My Fire Firesteel on my key chain.