What are the various miscalculations and mistakes McCandless made in chapters 16 to 18?
Despite wanting to live in the wilderness, Chris McCandless was ill-equipped to do so. His unfamiliarity with the Alaskan climate and landscape would have been better addressed with some preparation beyond his acquiring a book on the local plants. Krakauer's description of Chris' decision to learn about berries from books suggests he was fairly naive about what it would take to survive in the wild and avoid starvation. His lack of basic knowledge that most wilderness hikers would find crucial (how to attract attention in an emergency with flares, for example) and his failure to equip himself with emergency gear and food supplies led to his death by starvation (or possibly by poisoning, as he may have eaten plants he did not identify properly, but this was not fully determined). Although there was evidence described by Krakauer that Chris did some hunting, he obviously did not have the supplies or knowledge of preserving meat by drying, salting or curing it, which would have helped extend his food supply.
Chris also miscalculated his situation by willfully isolating himself from others who may have helped him, despite being not very far from civilization (only 30 miles from the highway and 16 miles form a hiking path). By not disclosing his whereabouts to anyone, he made it virtually impossible to maintain contact for emergency services to discover or rescue him.
McCandless is left behind and for a while cannot secure another ride as he takes much time to soak in the Liard River Hot Springs.
He ignores Stuckey’s advice about the snow. Stuckey tells McCandless that he has arrived too early and the snow is still thick on the ground with no vegetation. He also does not inform his parents of his whereabouts as advised by Stuckey.
He does not get a map of the area and fails to cross the river which was passable one mile upstream.
McCandless makes another mistake by spending his time hunting and foraging which leads him to burn more calories than he consumes.
He makes the mistake of eating potato seeds that may have been covered in mold that affects energy intake and so causes starvation.
In the book "Into the Wild" McCandless made many significant mistakes that led to his death. He had a truck driver drop him off at the entry point into the Alaskan wild. Initially he had a map with him but seemed to have purposely left it in the man's truck. The man stated that McCandless did not have proper attire or enough supplies. Chris had brought with him some basic items he needed which included a book on plants.
It is believed that Chris mistook and ate some berries that were poisonous that may have caused him to have rapid dehydration. He did not anticipate that the river would climb and become so rough that he could not cross it. In addition, Chris had no map with him. Had he had his map, he would have known that he was not very far from a safe route out of the wild and could have lived.