Other mistake: The closing captions state that Chris McCandless' sister Carine flew "his" brother's ashes home, instead of "her" brother's ashes.
Other mistake: When Chris is sleeping in his yellow car during the thunderstorm, he gets hit by a flash flood. Afterwards he abandons his car and removes his licence plates. His plates are: UW4-924. A few minutes later his parents decide to visit Chris in Atlanta. We then see a shot of a white car on the freeway, which has the exact same licence plate (UW4-924).
Answer: Chris probably knew what his Social Security Number was, and providing this could be enough to legitimately get him on the payroll. The people he worked for along the way could have been used as references. It is also possible that he was able to get a transcript and/or other documentation from Emory University; maybe a phone call to check if he graduated was more than enough. Christopher was also somewhat older and educated/ intelligent than others seeking such employment - in his early 20s compared to high school kids - which may have given him an advantage. There was probably a high job turnover rate among the employees, making it easier to get hired. Fast food restaurants tend to hire people from all walks of life, many who do not have much, if any, formal education or prior job experience; they often hire whoever applies.
KeyZOid
Not entirely disagreeing with your answer, but having worked at a university, I can say that someone cannot simply make a phone call to obtain a student's academic information, even their own. A 1974 U.S. federal law (FERPA) protects student privacy. Every school is different, but there is usually a process requiring identification, paperwork, and signatures to prove identity. As Chris had left all his I.D. behind, it would take some time for him to get any college information, particularly from a school in another state.
raywest ★