I do carry a second second butane lighter. And a pressurized one. And matches, because if I have to, I can bundle a few of them together and light them with one- hotter! And a ferro rod (actually, everything backs this up). And usually a second thing of matches. And a frensel lens. And cordage so if I've got nothing else other than banging rocks together, I can try a fire bow again. And I can bang rocks if I really need to. And there is tinder in my gear, usually PJ-balls and/or tinderquiks, jute, and candles.

Lets just say I LIKE being warm. And I might like fire. *laughs*

As for why one might carry a fire piston, because they are cool. My inner pyro and the scientific sides of my brain both giggle gleefully at the concept. But I wouldn't carry that as my only source of fire.