I am pretty sure that no cheat sheet could have helped because I suspect there was no answer key. The "grader" would simply point at the response to more difficult or ambiguous question and say "that's not the right answer, therefore you fail." If an applicant did have the temerity to ask what the correct answer was, he would be told that it is against the rules to provide correct answers to applicants who failed.
ETA
On second thought, failing people was even easier than I described. Given that few rural black residents of Mississippi would own a watch, the test administrator would simply wait until six or seven minutes had passed and say, "Time's up. You didn't finish, so you fail." With that approach, the test administrator himself could be illiterate.