We used to waste leftover veggies, throwing them away or putting them in the refrigerator until they're old enough to throw away.
Now, when we're done with dinner and there's anything from 2 T. to a cup (or more) of veggies left over, I spoon whatever leftovers I have into a gallon-size freezer bag. I keep a running bag in my freezer.
Once the freezer bag is full, I make soup! Never the same twice, and I don't feel like I'm wasting food.