The most challenging part of the whole shoot was filming McCandless's final days of starvation in Alaska.

HIRSCH: Everyone pretty much left me alone. So a lot of those scenes are me deciding what to do in that moment as though I was really living out there. I'd be cold and freezing and hungry. But the discomfort and the harshness helped me relate to what Chris had gone through. I lost 41 pounds. I'm five foot six. I went from 156 pounds to 115 pounds. They gave me a couple weeks off. I had to gear up to do it, you know? [I'd do] two hours of cardio a day on very few calories. I had teeny bits of food every day. I went to a level of hunger I had no idea existed. We shot for two weeks like that.

HILDEBRAND: Towards the end it was torture for Emile. He was really emaciated. We shot his death [in August], and it was 12 hours from the time McCandless died. It just happened that way.