Krakauer's life and McCandless's life are similar in a few ways. Concretely, there is the similarity that both men decided to venture out, alone, into the wilds of Alaska. Both men did so at relatively young ages as well.
Another similarity between Krakauer and McCandless is their relationships with their fathers. During college, McCandless quickly became disillusioned with his father. As a result, McCandless began distancing himself from his dad and developed an aversion to his father's financial support. For example, McCandless ended up donating his remaining college money to a charity. Krakauer doesn't go into detail about his own father, but he does admit that he feels kinship with McCandless because of their father issue.
But I believe we were similarly affected by the skewed relationships we had with our fathers. And I suspect we had a similar intensity, a similar heedlessness, a similar agitation of the soul.
A key difference between the two men though is that McCandless, by all accounts, was not likely to ever return to civilization. He was too much of an idealist for it. Krakauer, on the other hand, is more of a realist. He realized that while he enjoyed his adventures, he ultimately saw them as exactly that -- adventures. Not a way of life.
Krakauer and McCandless have very similar lives, hence Krakauer's interest in Chris's story.
Krakauer, like McCandless, went out on daring escapades in which his life was in danger (he fell through an 'ice bridge' once and nearly dropped into the ravine below!). He also did not have the best relationship with his family (dad, in particular), just like Chris.
However, Krakauer makes it clear that he is NOT exactly like McCandless in that he knew when to stop; he was able to realize that he was not willing to die for his adventures.
Krakauer points out that McCandless was not "crazy" as some people had dubbed him, and he uses himself and several other "extreme" adventurers to make his point. He says that all of these men, including himself had an unlimited imagination and a profound love for challenges and the outdoors.