I am sure we all agree that the most important thing you can have with you in a survival situation is your wits and a little forehand knowledge, but what about what we have to pack with us? For most, I'd guess it's either going to be firemaking or a good knife.

I think the most important tool is a good knife. Even just a single small blade pocket knife significantly increases my odds of success when mixed with a little ingenuity. I can't think of one thing that would have as much influence on my outcome as having some sort of knife. It is the one thing I would have the hardest time getting along without.