Happy Halloween to all!
There’s no better time to point you to the LOC’s “Wise Guide” for October, which explores how trick-or-treating got started:
The origins of present day “trick-or-treat” date back to the Celtic tradition of offering gifts of fruits and nuts to appease wandering spirits. If not placated, the villagers feared that the spirits would kill their flocks or destroy their property. Others trace “trick-or-treat” to a European custom called “souling.” Beggars would go from village to village begging for “soul cakes” made out of square pieces of bread with currants. The more soul cakes the beggars would receive, the more prayers they would promise to say on behalf of the dead relatives of the donors.
The Wise Guide includes links to other Halloween-related resources at the Library of Congress.