The college library had dollar changers for use with the photocopy machines. I had a friend who made the discovery that if he copied both sides of a dollar bill and glued them together with some rubber cement that there were older machines that would give him change. So in exchange for two nickels investment he'd get back four quarters.
He literally lived on this hack for an entire year. Course this was 40 years ago and those 'older' change machines were probably some of the first ever built and not very sophisticated.
Why it took the college a year to upgrade the machines I will never know. He wouldn't have been that hard for the police to find. All the local bartenders knew as the quarters guy ;<).