I have gradually over the years switched my thinking from cleaning my plate to not taking more than I can eat. If it is an unknown food at a buffet for example, I'll just take a taste so as not to waste it if it doesn't agree with me. With all the curbside/to-go meals that we order, if I have asked for no bread/chips/pitas and they include them, I do not feel bad throwing them out. If someone else is serving me and it is way too big a portion, I'll ask to start out with a smaller portion, or just truthfully say that it's more than is comfortable for me to eat, or even express my appreciation then ask if I can take the rest home, like in a restaurant. I am never personally offended if someone doesn't eat what I serve, so I assume the same when I am the guest. I disregard any judgmental or unkind reactions, because those who react that way are not my people.

I'm working on only having portions in front of me. The challenge is when eating out. So many restaurants make over portion sizes for their menu. When logging away from home meals, I try to find the nutrition info online. If it's as much as I think it is, I adjust the rest of my day. I am learning to take only what I can eat. I guess I'm avoiding waste (waist) by not taking too much food to begin. I have stopped getting fries or other side items. If I eat out, I try to just get the main item (protein) will a little of the other as a bonus. I have no issue throwing away fast food I don't eat.

Interesting conversation. I agree, I don't have an issue with throwing out food that I pick up from a fast food joint. What I often do if I have too much on my plate at a restaurant I will take it away and have for lunch the next day. I also never eat food I don't like. Life is too short. I try not to put myself in the predictament of having to do so if I am a guests. I tell people that I apologise but I do not do hot cream or dairy type meals. So it never makes it to my plate. BUT at home, I never throw food out and if I am alone (which I am most of te time) I have lunch with my left over the next day or make myself a small soup with the protein and add lots of veggies.

This was never a real problem growing up, coming from a large family, there were times I wanted more on my plate no matter what it was.
Maybe that set up my want of large portions.