I agree that gas is not really the best way to start campfires. With all the wood, lighters and matches I find, even Paris Hilton could start a fire at some point. I mean your character can make planks easily (maybe not very pretty planks) with a saw and log off the bat, So lets say he has the basic understanding of how to start a decent campfire without just dumping gas on a pile of sticks. If anything, you could tie it into cooking and give it a timer on how long it takes depending on skill.