Well he had a .22 rifle
it's kind of amazing he managed to kill a moose with it!, but there is one of the skills he lacked, the know how to preserve meat but to be fair he went off the advice from his South Dakota friends and tried to smoke the meat when it would have been better to cut it into thin slices and dry it.
What I took from McCandless story is his very confused relationship with his father, and that was the driver in pushing him to attempt the "heroic gesture", and perhaps drove him to remain when it would have been obvious to most other people that he was in extreme danger early on.
Well he actually managed to survive long enough to be satisfied with what he did out there and he did
try to leave, the early season melt is what kept him there, then of course the mold on his seeds made him sick and finished him off.
What I find really foolish is his original plan that the movie did not cover was to walk cross country for 500 miles, this plan is nuts when you consider the horrible marsh terrain of early spring and the fact that finding enough food is a full time job by itself but to add traveling and the calories burned from doing so? he spent the night in the bus then traveled for two days and realized how bad his plan was so he returned to the bus and stayed.
