You don't have to be a rocket scientist (or an English teacher—here at Shmoop we think they're pretty smart, too) to figure out that Brian's hatchet is an important little item in this book. His hatchet helps him build a fire, cut branches for his shelter, and make the tools he uses to catch animals for food. Without his hatchet it's a pretty safe bet that Brian would have been bear breakfast within just a few days of the plane crash.
If it weren't for the hatchet, in fact, the book might have been called something like Brian's Very Short Adventure. Or maybe Brian is Eaten by a Bear. Or Brian Survives a Plane Crash Only to Perish Slowly in the Woods. Bummer. So calling the book Hatchet kind of makes sense, huh?