Today in 1974, US Patent 3788538 A was issued, an invention of William A. Kuenzi, assigned to Miller Brewing, for his “Beer Carton.” Here’s the Abstract:

The entry of light into the interior of a beer carton through the handholes thereof is prevented by flaps, one of which is hingedly attached to the inner surface of each end panel above the upper margin of the handhole. The flaps are preferably wider than the handholes, extend downwardly below the lower margin of the handholes, and have a free lower edge. The flaps are preferably deflectable inwardly along a fold line opposite the upper margin of the handholes to permit entry of fingers around the upper margin of the handhole and between the inner surface of the end panel and the adjacent surface of the flap. Each end wall panel is preferably made of triple-folded material with the flap being cut out of the inside face of the material and the handhole being cut through the other two thicknesses.