There is reference in the book to two pairs of boots that Chris wore for a long period. In the beginning of the book, Chris hitches a ride in Alaska with an electrician named Jim Gallien; Gallien notes that Chris's boots are not waterproof or insulated, both of which are vital for preventing frostbite in cold climates. This pair of boots is later mentioned by Krakauer as being:

...Kmart hiking boots... arranged neatly beneath the stove, as though he'd soon be returning to lace them up and hit the trail.

The boots were cheap and useful in Southern climates, but were entirely unsuited for the cold North. Chris probably didn't even think about the necessity of keeping his feet warm and dry, or he would have purchased a better pair before leaving for Alaska. Gallien took pity on Chris, and knowing that he needed something better, gave him a pair of old rubber work boots:

"They were too big for him," Gallien recalls. "But I said, 'Wear two pair of socks, and your feet ought to stay halfway warm and dry.'"
(Krakauer, Into the Wild, Amazon.com)

This pair of boots is later revealed to be Xtratuf brand, and Chris used them to good advantage when crossing various rivers and streams. Without the boots, it is likely that he would have lost toes to frostbite very quickly in the freezing cold of the Alaska wilderness. Both pairs of boots were found in the abandoned bus along with Chris's body.