I read in the news that more and more college cafeterias no longer offer trays for you to put your dishes on. Various reasons have been given- one is that it makes the cafeteria seem more home-like and another is that it saves water since trays no longer have to be washed.
An added benefit seems to be that it reduces food waste. You can pile a lot more food on a tray than you need. And, human nature being what it is, once that food is in front of you, you are pretty likely to eat more than you need. Have you ever noticed that you eat too much at an all-you-can-eat buffet?
The solution? Not using a tray is a good one. Otherwise, try not to serve yourself too much food. If you do make the mistake of taking too much, don't make a second mistake and justify eating it by saying, "I can't stand to waste food". Better to compost the food than to make your poor body deal with it.