Trick or Treat!

The earliest attestation has now moved to 1927, in an Edmonton newspaper, I learned here. This story quotes the original article:

Halloween provided an opportunity for real strenuous fun. No real damage was done except to the temper of some who had to hunt for wagon wheels, gates, wagons, barrels, etc., much of which decorated the front street. The youthful tormentors were at back door and front, demanding edible plunder by the word “trick or treat”, to which the inmates gladly responded and sent the robbers away rejoicing.” From ‘Trick or Treat’ is Demand,” Herald (Lethbridge, Alberta), Nov. 4, 1927