describe chris's life on the stampede trail

Do you mean chapter 18? Chris lives in an abandoned bus. He is ill equipped and rather ignorant of wilderness survival. McCandless manages to shoot small game here and there, and forage for some berries, but the poison in his system makes this food useless. He takes a last picture of himself in front of the bus, holding his farewell note, and then crawls into his sleeping bag and at some point in the next few days, dies.