In "Fahrenheit 451", what purpose do the inhabitants of this wilderness have for life?What is the purpose of the men in the wilderness in the last chapter of Ray Bradbury's Fahrenheit 451?
There are a couple of ways to look at your question. The first (and easiest to answer) is what purpose did they have to the story?
The men wandering outside of town are the other Fabers and Montags and Clarisses---people unwilling to submit to a group mentality and therefore targeted by the powers that be. Without them, and others like them, humanity would kill itself off with high speed car crashes and nuclear wars. These are the educated, the educators, and the philosophers who held civilization in safety until society was ready for it again.
The second perspective is more philosophical and universally relevant. The wanderers (also called the "book people") represent that part of civilzation that holds fast to ideals and principles and thought. Every culture has its "book people." Ancient cultures all over the world had oral traditions that handed down history and artistry from one generation to the next. The Dark Ages had the priests who saved much of ancient art and literature. The 20th century had the rise of technology that allowed vast amounts of information to be stored in very little space. No matter how apathetic or corrupt or uneducated the general populace may be, there are always those who seek to preserve the things that set humans apart from animals: philosophy, creativity, curiosity, order, and reason.
As Granger said to Montag, "...that's the wonderful thing about man; he never gets so discouraged or disgusted that he gives up doing it all over again, because he knows very well it is important and worth the doing."