Chris is a strong-willed, charismatic character. He is a young person with decided opinions and heartfelt convictions, who has been heavily influenced by anti-establishment, idealistic thinkers such as Thoreau and Tolstoy. Chris is the type of person who acts decisively but without necessarily thinking through the consequences of his actions. Late in the story, for example, he heads out for the Alaskan wilderness having thought through some, but not all, of the dangers. 

Chris is a person of strong passions. If he likes you, he pours himself out generously and makes himself very likable. If he doesn't like you, he cuts you off completely and coldly—as he does with his parents, revealing little sensitivity about how much worry or pain he might be causing them. He tends to feel he knows he is right and has no problem lecturing much older people on how they should be living their lives.

Chris's personality is a mix of heady, enthusiastic optimism and a full embrace of "sucking the marrow" out of life. As he is dying, he journals with mature wisdom, generosity, and acceptance. He also displays youthful impulsiveness, a risk-taking mentality, and withering judgments of those, like his father, who are materialistic and do not think as he does. 

Chris was a typical young man who had lived a typical life. He grew up in relative comfort, perhaps even a bit sheltered, from the harsh realities of the world.

Like many college students, he wanted to journey and experience life at its most basic level. I would not describe him as foolhardy as much as I would say that he was inexperienced and ignorant to the harsh realities of the power of mother nature. Many young adults just don't recognize or fully appreciate that, yes, they can in fact die, even at the age of 22 or 23. That lesson comes with age and life experience.

Yeah...I suppose he seemed well adjusted, althletic and bright but I would describe his personality as shortsighted and foolhardy.

David Henry Thoreau's Waldon Pond was just miles outside of Boston. In fact, from some places near the pond, you can see the city. This was NOT the case for Chris. He was hundreds of miles from a big city in the middle of possibly the most wild national park in all of the US.

According to the reminiscences of his family and university friends, McCandless was a seemingly well-adjusted twenty-two-year-old at the time of his disappearance. He was athletic, bright, and a natural-born entrepreneur, excelling at so many things that he tended to be overconfident. A double major with above average grades, he led a life of comparable comfort and good fortune. He worked on the student newspaper at Emory University and, like many other people his age, thought about injustice in the world around him

What are quotes from the book Into the Wild best describe Chris' characteristics?

There were many individual characteristics that combined to form the complicated person who was Chris McCandless.  Because of that, there are many quotes and passages that reveal various aspects of his personality.  Fortunately, some passages provide information and insights regarding multiple characteristics.  One such passage addresses the beginning of Chris's adventure:

...The trip was to be an odyssey in the fullest sense of the word, an epic journey that would change everything.  He had spent the previous four years, as he saw it, preparing to fulfill an absurd and onerous duty: to graduate from college.  At long last he was unencumbered, emancipated from the stifling world of his parents and peers, a world of abstraction and security and material excess, a world in which he felt grievously cut off from the raw throb of existence.

Driving west out of Atlanta, he intended to invent an utterly new life for himself, one on which he would be free to wallow in unfiltered experience..he was now Alexander Supertramp, master of his own destiny.

On another occasion referred to in the book, Wayne Westerberg's mother discusses a side of McCandless that provided motivation for his undertakings.

"There was something fascinating about him...Alex struck me as much older than twenty-four.  Everything I said, he'd demand to know more about what I meant, about why I thought this way or that.  He was hungry to learn about things.  Unlike most of us, he was the sort of person who insisted on living out his beliefs."