As you probably already know, presenting gifts to gods is an ancient practice that was usually meant to appease angry gods, or to act as a payment for a request or prayer. In the case of fountains and wells, people would toss in a coin while sending up a prayer—an early version of making a wish.
(uncountable, Oxbridge slang) The activity of pennying in general, as part of a meal or drinking game, whereby dropping a penny in a person's drink means that they must finish it (or some such variation thereof); commonly associated with crewdates at Oxford and swaps at Cambridge.