There are lots of ways to stretch food. In soups you can add more milk or water or broth and throw in some beans or pasta or veggies. Essentially, I guess, you're making more soup, but it stretches the original batch none the less.
Casseroles are great for using leftovers, rather than tossing them out. I don't know about you, but I almost always have at least a serving and a half left over after a meal. Not enough for another meal, but too much to throw away. We also have leftover nights where we clean out the fridge and everyone gets their favorites while not having to suffer through things they didn't like the first time 'round.
Since we're talking about servings...did you know that a bag of chips (at least the one that's still in my cupboard) has 11 servings! Scott and I could easily finish a bag off between the two of us. When we started Weight Watchers and, therefore, started paying attention to serving size we found that things lasted much longer. That stretches the dollar I pay for groceries quite nicely.
My last idea isn't for everyone. But sometimes I just don't feed the kids.
They have gotten fussy and finicky and picky and particular and many other great descriptive words I could come up with. So, rather than putting a scoop of some side dish on their plates to get looked at funny, I put a fork full. They still won't actually try a full fork full, but I'm wasting a lot less that way. If they actually, by some alignment of the planets, like whatever decorated their plate they are welcome to more.
Now, of course, this creates even more leftovers, but at least they can actually be eaten or made part of a casserole, soup, wrap...something. If they get scraped into the trash, well, then no one gets them and I might as well toss my pennies away too. It's actually probably more like quarters with these three!