1/2 of people received large bucket of popcorn for movie. 1/2 receive medium. On average, recipients of the big bucket ate about 53% more popcorn, even though they didn't really like it. After the movie, when asked if they are more because of the bucket size, replied, "Things like that don't trick me."
Similar study with soup: when given a soup bowl that automatically refilled itself, no matter how much people ate, people would just keep eating...not paying attention to how much it was.