My mother was from the old school. Leftover food was given to the family dog. However, that is not likely to be possible in todays pet who is well brought up on food prepared especially for him. That means that moms solution to leftover food no longer holds water, and the problem persists. We can always fall back on the old saying, waste not want not. That surely is applicable to leftover food. The best thing to do with leftover food is to make it accessible to be eaten on the same day that it became a leftover. Food that is packaged in plastic containers or wrapped in foil and frozen will most likely be thrown out when discovered several months later, hiding in the freezer. Food that is laid out on top of the range in open view to anyone who passes by through the kitchen looks like a smorgasbord. What does one do with food found in a smorgasbord? Well, eat it, of course.
The average housewife probably considers herself frugal when she packs up that leftover rump roast to be brought out some other day and served with fresh peas. But, her family in the meantime has digested her marvelous dinner and is loading up with potato chips, candy and the like. She has to stretch her food budget to pay for snacks while conserving that rump roast that could have been sliced, left on the range with some sliced bread and a dish of mayonnaise as if to say, are you still hungry. Eat it.
The frugal housewife will not even realize that she is actually being nicer and kinder to her family by offering healthy food in place of snack food. She probably will not even realize that she is saving money in snack food by offering her family food that she has already spent the family budget on and that is already available to be consumed. The enjoyment of fresh leftovers is not to be belittled. Everyone loves a sandwich much better than chips, well, sometimes. There is a place for everything and everything in its place and that includes leftovers. They should be made attractively available to be consumed on the same day that they became leftovers and only packaged when the eaters have gone to bed.
That is the only thing to do with leftovers unless the cook is hungry and finishes them first.