I think it’s good practice to appreciate the food you have but have come to the conclusion that it is silly beyond a certain point to fret over “wasted” food (although I still do, since it’s a pretty well ingrained habit). Much of that change of thought is dependent upon putting “wasted” food in a different or broader context. For example:
“Clean plate” people who are overweight (myself included) waste food twice by a) eating calories they don’t need and b) having to expend extra energy to lose the weighty they’ve gained from the extra calories.
We grow more corn than we and all our feed animals can consume. We grow so much corn, that it’s cheaper in Mexico to buy U.S. corn than it is to buy Mexican corn.
The U.S. just recalled 4.9 million pounds of beef for E. coli contamination, which would not have happened if processing was less centralized. Repeat ad infinitum for all other manner of processed agricultural products (like the peanut recall in recent years).
I guess my point is that respect and appreciation for food are important, but it’s a bit naive to simply take on the liability of guilt over what is left over on your plate or in your fridge or at a pot luck. The table is much bigger than our immediate perceptions and is tilted so much that unless we broaden our view we are deceived into thinking of it individually as “our” waste. Food is overproduced for reasons of “national security.” The animals and plants that make our food are manipulated by food producers to maximize profits and not nutrition. Corporate interests under the guise of U.S. “aid” (and other interests and their correlated mechanisms) systematically subjugate third world nations through economics and sometimes through deliberate manipulation of the food supply (“If you control oil, you control nations. If you control food, you control people.”)
As far as I’ve discerned, the way out of the above dilemma is to eat local and from smaller producers.
Another response to this question is to marvel at our abundance. In the 50s and 60s we were dazzled by promises of the World of Tomorrow with all the convenience, luxury and leisure we could imagine. Well, don’t we (the western “we”) have that today with food? Calories are cheap and plentiful. We have way more than we possibly need and way more than we can possibly consume (although many of us do try our best). One might argue that’s another reason to prioritize higher quality in our food presuming we can afford it, but if we can’t at least “enough” calories are relatively easy to come by.