Who are the members of the group Montag meets in the woods? How do they think of themselves in Fahrenheit 451?

They are people Bradbury refers to as "book covers".  They
each have memorized a book and plan to store the information for future generations that
will need it.  They think they are essential to society because they are the last
carriers of the information stored in books that society used for so many centuries. 
Without any one of them, a huge information gap would form that could never be
restored.  No book can be rewritten in its original form; therefore, these people hold
the last link to the invaluable knowledge contained in the books.  This group hides out
in the mountains until the bombing is over, and then it is up to them to re-enter
society and pass on the knowledge they have acquired.