It makes sense to carry a spare in a pocket where you'll always have it.
Years ago there was a group of hunters floating a remote river in Alaska. Here's the story to the best of my memory... They came around a corner with a heavily loaded raft and hit a sweeper which flipped the boat and dumped them into the cold water. In an instant their trip went from a fun time to the very definition of life and death. I think there were about four guys. Luckily no one was "pinned." Some were swept far downstream. They ran up and down the bank yelling and frantically trying to find each other. Miraculously, all survived. But they were out there, tent long gone, tarps long gone, sleeping bags swept downstream. They had nothing but what they were wearing. At least one didn't even have shoes. They were soaked and shivering. Matches and lighters gone with their gear. This was before sat. phones and Spot.
Just about when they thought they were out of luck, one guy remembered he had a lighter in his shirt pocket. His wife had given it to him and made him promise to keep it there. They got it working and started a fire. It was days from the time they flipped until they were rescued. At some point another group of hunters came downstream and gave them a tarp and some food. That one lighter saved their lives.
On trips of moderate lengths I carry two lighters. I try to never depend on fire to save my life. In other words, carry what I need to carry and do what I need to do to avoid getting too cold without outside heat.
For really long, remote trips where I can't resupply I'll carry at least three ways to start fire. Redundancy makes sense when firestarting tools are so light.
