To Build A Fire
One lesson is to not hike alone. Because with more than one person, it is easier to build fires. "He picked it (the matches) up in his teeth and scratched it on his leg." If there were two people, one person could strike the match on the other person's leg. "Then the man drowsed off into what seemed the most comfortable and satisfying sleep he had ever known." In other words, he froze in his sleep and died. If he had hiked with another person, they could have waken him up. "His theory of running until he reached camp and the boys had one flaw in it: he lacked endurance." In this part of the story he's feeling depressed and that he won't make it. He could use a partner for moral support.