why not keep track of how much food my guests actually ate, and try adjusting the amount of food at my next party to match?
I guess there is not a fixed amount of food brought per guest, but rather a random distribution. The host's goal is not to make sure that the average "food brought" equals the average "food desired", but rather that with, say, 95% probability the current "food brought" is at least 90% of "food desired" (feel free to change the numbers to fit your experience). Also, the host is hedging against the possibility that the few guests who usually come with hands full of food, suddenly can't come or for some random reason come empty-handed.
There are charities that focus on "recycling" food waste
I guess the best way to improve the world is to have a list of such charities in your neighborhood ready in a printed form, and give it to the host if they are interested.
I agree with all that and would add:
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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