The purpose of including the descriptions of items left behind by McCandless is: "To illustrate the respect with which travelers in that part of the world treat others’ belongings." (Option C)
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What is purpose?</h3>
The intent with which a thing was done, made, or said is called it's purpose.
Thus be highlighting the items that were left behind, the author describes how much respect people have for the property of others.
For example, your friend smoke with another peopel that you don't know and he want you to smoke, too. So would you smoke or not. Most of the time, people smoke because of peer pressure and then it became an addiction