Following in my mom's footsteps. I always cooked more than needed for one meal; and did not call it leftovers as it was meal planning. On Sundays, I would cook a couple of large meals: one was for Sunday's dinner; then we alternated those meals through the week, adding salad and fruit as needed. For decades, a pot of soup made on Sunday was my lunch for the week. As I live alone now, I still cook bigger portions and freeze half; then I can alternate weeks of meals. The result: nutritious meals at a lower cost; no waste.
I was raised by parents who grew up during the Depression and then had to scrimp and use during World War II. That mindset carried over as they had three more children after the war.
My guess in looking back is that for more than half the time until I was a teenager, we ate leftovers. Mom would make a big pot of something and we'd eat on that for days - either a stew or lima beans and ham or whatever. Our variety sometimes came in the form of the whole wheat bread that she'd make from scratch and bake every couple weeks. Besides having a slice or two as a side to the pot-cooked meal, we'd have what Dad called bread-and-with-it alone sometimes just for the meal. The latter meal might consist of bread, butter, and honey. Peanut butter was good back then, too, but we didn't always have that on hand.
Our breakfasts weren't usually from those, but sometimes, we could talk Mom into making cinnamon rolls from some of the bread dough. We'd eat a few of those with a glass of milk for breakfast for a few days until they were gone. Or, she'd whip up a large batch of whole wheat waffles and we'd use that batter for 2 or 3 days' breakfasts. She'd sometimes use sour milk in the recipe, just because we hadn't drunk as much as intended when we bought the raw milk from local farmers. Some had turned before we could finish drinking it or maybe one of us kids left it out of the fridge too long. I actually crave that sometimes, but settle for making myself regular, freshly ground whole wheat waffles when I get that craving.
I could go into quite a bit more detail about how we ate, but the main thing is that we didn't turn up our noses much at pretty much anything that was placed before us at the dinner table. (Mom's quote: "I'm not a short-order cook!") Very little of it went to waste.