Question

what can I do to persuade friends them not to waste food

Answer 1

You should tell him about the poor people who do not get 2 times meal.
You should also tell him about the result of wasting food .

Answer 2

U should tell them that a fancy meal that they eat at one time the poor cannot even get half of it. Instead of wasting food tell them to give it to the poor in a plastic bag or in newspaper.