I'll take Pathos to mean 'a quality that evokes pity or sadness' and in that sense, there are many examples in Into the Wild, the following being just a few:
1. At the point at which McCandless leaves Wayne Westerberg's farm for the last time, we learn that he got drunk on his final night, had a wild night in which he revealed for the first time that 'he knew how to play' piano, a brief demonstration of a talent that he had honed for many years but that he was too modest to show. This is made pathetic (in the true sense of that word, i.e. full of pathos) when he then cries at the point of his departure the next morning at the end of Chapter Seven. His tears invoke a sense of his own knowledge of the risks that he is going to take which is when one of his fellow farm workers "started to have a bad feeling that we wouldn't never see Alex again." He is clearly well liked and people wished greatly to know him better; he has the capacity to create joy in others, an element of pathos that we feel as a result of his demise.
2. There is a good deal of pathos to the scene before his departure from the Slablands RV area when he is on his final night in Jan Burres's RV, watching 'an NFL playoff game' on TV. Burres notices that he was 'rooting especially hard for the Washington Redskins' and she asks him if that's where he is from. He tells her that he is but, despite spending considerable amounts of time together over weeks, she claims 'That's the only thing he ever let on about his background'. It is clear that throughout this whole episode, McCandless has both considerable warmth and consideration for others but is only able to connect with people to a certain extent due to the self-imposed distance he placed between himself and them.
3. Westerberg discusses McCandless's naivety during his stay with them, describing him as having 'gaps in his thinking' such as the occasion on which he attempted to cook a chicken in a microwave over and left it full of grease as he could not figure out that the grease had nowhere to drain. There is pathos to this event particularly because if such everyday things are at times beyond the romantic but slightly impractical McCandless, this incompetence foreshadows that which leads to his demise in Alaska where, despite being skilled enough to survive alone for a while, his oversights limit his chance of survival.
4. For all of his dislike of the commercial world and self-abasement with menial manual labour, there is tremendous pathos to the account of McCandless's commercial acumen and salesmanship. At the end of Chapter 11 we discover, for example, that he worked for a local building contractor in his home town who had 'offered to pay for Chris's college education' if he would continue to work for him. It is particularly poignant that if Chris had been able to reconcile himself to his capacity to earn money, he might have done more of the good and, long-term, have bought more freedom for himself and others. The tremendous potential he had makes for greater pathos in his demise.
5. There is tremendous pathos to one of the very small accounts within the book from McCandless's time working in McDonalds. We discover that part of his self-imposed difference from others is a dislike of wearing socks. When questioned about this and told that he must wear socks if he is to be employed, he agrees for the time that he is working but 'as soon as his shift was over, bang! - the first thing he'd do is peel those socks off'. The pathos of this scene is two-fold: that an Emory graduate maintains such moral integrity that he will live his principals so fully that he will work at McDonalds in order to maintain his absolute freedom might inspire sadness in some. However, perhaps more poignant still is his willingness to accede to corporate rules only until the moment his shift ended, as if the wearing of socks required such an act of will that it constrained him. It is full of pathos that a young man felt the need to maintain such distance from himself and conformity that he had to make ever grander and more protracted statements of difference that eventually led to his death.