In Chapter 17 of Into the Wild by Jon Krakauer, what important guiding tool does Chris get rid of?

That chapter is a really difficult chapter to read, emotionally at least. I may have thought that McCandless was a bit crazy at different times throughout the book, but I always admired his ability to survive on so little.  I may have thought him odd, but I also never thought him stupid--until Chapter 17.  The guiding tool that McCandless chose to do without while on his Alaskan adventure was a topographic map.  Had McCandless had a topographic map of the area surrounding the bus, he would have seen that he was close to a USGS gauging station.  The gauging station had been decommissioned, but it still had the cable crossing in place to allow transit across the river.  Had McCandless had the topographic map, he would have seen how close he really was to being able to survive.  

When McCandless tried to walk out of the bush one year ago the previous week, the basket was in the same place it is now, on his side of the canyon. If he’d known about it, crossing the Teklanika to safety would have been a trivial matter. Because he had no topographic map, however, he had no way of conceiving that salvation was so close at hand.