There isn't really much to do about this, except to inform the students about calorie intake. If they know that they shouldn't be going to the snack bar every day, then hopefully they won't. Also, there should be a limit on how much one person can buy. Three cookies and five bags of chips are very unhealthy. It doesn't matter what they're made of, it's just too much food.
Check out a quick presentation on MyPlate below! It will give you some good tips for healthy eating in the future.