One good quote comes from the letter that Chris sent to Ron Franz, encouraging the older man to experience new things:
So many people live within unhappy circumstances and yet will not take the initiative to change their situation because they are conditioned to a life of... conformity...
This quote shows how Chris viewed the "safe" life that society expected from him and from others. Chris wanted to challenge himself and his ideas, to pit himself against the world regardless of what other people thought, and especially to avoid what he saw as the endless trap of routine. By becoming a nomad, Chris forced himself to adapt to new situations almost daily, and so escaped the daily grind that he saw as detrimental to personal growth.
Another good quote comes from a letter Chris wrote to his sister, explaining some of his passionate irritation with his parents:
Since they won't ever take me seriously... I'm going to completely knock them out of my life. I'm going to divorce them as my parents once and for all...
(Krakauer, Into the Wild, Amazon.com)
This quote is less about Chris philosophies and more about his dissatisfaction with the role that his parents expected him to play. Chris fought against the ordinary lifestyle that his parents enjoyed all his life, and with this letter, he explains that part of his intent was to "punish" them for their constant nagging. By vanishing, Chris sent a message to his parents that he was never going to play their intended role, but he also sent the message that his path through life was not already written, that he was going to forge his own path whatever the cost.