Given the weight of a decent firestarter vs. how valuable it is, I always carry several sources. Plain old wooden matches stashed here and there (both normal and weatherproof), a lighter or two and a magnesium starter.

I also put them in different layers of my clothing, just in case! You never know what might happen to a pocket or even a jacket out in the bush. Hypothermia is a horrible thing and the first item to normally go is the jacket.