I am very happy to answer you this question. I often see at restaurants that people order more then their capacity to have. so i suggest that their must e some kinds of bins that separate the good food which can be eaten and if it is a non-veg dish the left out bones can be removed out so that they can be fed to some animals. this is a way we can control waste items of food and the good food which is fit for eating can be given to some poor people outside the restaurant.
one more way of controlling is the person of the restaurant must make a strict rule that ther must be no wastage of food and you will be have to pay fine when you waste. i some countries like Germany they call the police when you waste food.