Answer: 90 percent, according to a survey commissioned by Reese's.
One solution to this problem is the “candy converter” in New York City. Built by Reese’s, the machine was set up at Washington Square Park on 5th Avenue between 4 p.m. and 9 p.m. As its name suggests, the machine “converts” unwanted candy into Reese’s highly desirable Peanut Butter Cups.
A spokesperson for Reese’s said they expected the machine to dispense up to 10,000 cups. She also said the reaction from the public was incredibly positive, and that “maybe [Reese’s] will bring the Reese's Candy Exchange to other cities; stay tuned for Halloween 2019.”