In exchange, each individual presenting a luxury item would receive a piece of engraved silver plate (typically in the form of cups, bowls and spoons), which because it came from the queen herself, had a "value" far beyond its intrinsic worth.
To avoid dying in a famine, the brain is wired to pick up on signs that calorie-rich foods are nearby, which helps explain why that piece of cake on the plate in front of you is so irresistible, or why seeing a sign for a doughnut shop draws you in even when you know you need to watch your diet.