In an excellent social experiment, TCU scientists discovered that people were less likely to overeat when confronted with how long it would take to "walk off" the food they were eating. The study comes in the wake of the Affordable Care Act requiring calories be displayed on the food. The journal article can be found here
This image is from Scientific American's article on the subject. You can see how the calories "jump off the page" when confronted with the prospect of having to walk off everything you just ate.
You can use this exercise calorie calculator to see how long it can take you to burn off breakfast lunch or dinner with a large variety of exercises