All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
May Allah reward you for your goodness and desire to do it. You are not required to eat more than what you are able to eat lest the food may be thrown in the trash. However, you should advise those in charge of preparing and cooking the food not to exceed the amount of food needed. If you can keep the leftovers and eat them when needed, you can do that; otherwise, you may give them to a needy person or throw them to animals, for example. Indeed, this is a good deed because it involves preserving the food and avoiding the dispraised extravagance. If the leftovers cannot be used under any circumstances after adopting all these methods, you will not be sinful if you throw them in the trash in such case.
Allah knows best.