Fire

The Road's world has strong ties to fire. Modern society was completely destroyed by fire, and it is often used in the new world to hurt other people or in a terrible way. Take the Blood Cults, they often use fire to cook their meat, generally the flesh of other human beings. Or, people use to destroy buildings, homes, etc etc.. But for the man and boy, fire is something totally different.Fire serves as a protector; it keeps them warm, kills poison and whatnot that's in the canned food they heat, and at night, often helps keep the boy from becoming too scared.

But fire also is something different for the duo. The man often tells the boy that they're "carrying the fire." And from what I can see, they really are. Greek myth says that Prometheus carried fire down from Mt. Olympus and gave it to mankind. And then he got punished blah blah blah. That's not the important part. In a way, that's what the man and boy are doing in The Road. They're carrying a metaphorical fire. They're carrying hope (or basically any other positive feeling). The two are the only "good" people that are present in the story.