You might like to consider the way in which the various quotes that are used to introduce chapters compare Chris McCandless to Thoreau, particularly in the way that certain quotes were underlined in copies of books found with his body. For example, Chapter Twelve begins with the following quote:
Rather than love, than money, than fame, give me truth. I sat at a table where were rich food and wine in abundance, an obsequious attendance, but sincerity and truth were not; and I went away hungry from the inhospitable board. The hospitality was as cold as the ices.
The word "truth," we are told, was written in large letters at the top of the page. It is in this chapter that the author tells us about the relationship with his parents and the way that he perceived that truth was lacking, in particular with his relationship with his father.
Again, at the beginning of Chapter Six, a longer quote from Thoreau begins by saying:
No man ever followed his genius till it misled him.
Clearly, such quotes serve to implicitly compare the character of Chris McCandless to Thoreau, particularly focusing on the way in which the two rejected the stifling norms and conventions of society, and believed in following your inner soul and trusting on your own resources.