I agree - fire and sharps, the redundacny is very important. A knife can break, or be lost, your matches snap or the spring on your sparklite fail. It takes a hardcore woodsman (or a caveman) to be able to efficently make fire or edged implements. But with those tools, you could improvise just about everything else you need for survival.

Nearly my entire PSK is a redundant backup for items (sharps, first aid, firestarters, compass, water, food, light) that I normally carry on my person, but the small weight in my pocket relives a bigger weight off my shoulders - knowing that I have backups of the basic and essential items needed to sustain life, even if Murphy wants to play with my primary equipment.