1) He hitchhiked.
2) He drops Alex off in Fairbanks. He tells Stuckey he wants to go to the University to study what kind of plants he’ll be able to eat. Stuckey tells McCandless that he’s too early, there’s still two or three feet of snow on the ground, but McCandless is too stubborn to listen.
3) A gun, some shells, his backpack, 9 or 10 books, a fishing rod, 5 LBS of rice, and Jim Gallien's lunch.
4) His original plan was to cross the river, not knowing that once it thawed he wouldn't be able to wade back.
5) I believe three months.
6) He had preserved the moose meat incorrectly and it was filled with maggots. He said that he wished he'd never shot the moose, it was one of the biggest tragedies of his life.
7. When he attempts to leave the bush early, McCandless finds what was easily crossed in April is now a rushing torrent which would surely drown him, so he turns back, hoping if he waits it out it will again become crossable.