One of the most basic tenets that my parents drilled into me from an early age was "waste not, want not", especially where food was concerned. My mother was very good at saving and reusing leftovers -- what started out as vegetables from a beef roast usually ended up in vegetable soup, and likewise holiday leftovers were carefully repackaged and frozen for consumption months later. Of course, my parents both grew up during the depression, so such habits were strongly reinforced during their formative years, which is why they were passed on to us.
I wish I was as thrifty as my mother, especially now that the economy is in the dumps and everyone is cutting back, but I must say that I'm just not cut out for it. Leftovers in our house tend to be thrown out after a few days of being forgotten in the back of the fridge. However, one exception that I make to that rule is with leftover produce -- particularly carrots, celery, onions and leeks. When these start to go past their prime, I'm usually good about making them into one of the easiest, and best ways to use leftovers that I know of -- making homemade chicken stock.
First of all, let's review the difference between stock and broth. Stock is made from bones -- broth is made from meat. The difference is often subtle but you can usually see it when the two liquids are cold -- stock will jiggle a bit like jello -- that's because it actually contains gelatin that has been rendered out of the connective tissue in the animal products (bones and cartilage) that it is made from. The reason I like making my own is that (a) it tastes an awful lot better than the commercially packaged alternatives and (b) it's cheaper -- in fact, pretty much free if you use leftovers the way I do.
In fact, what I do with my chickens is that I freeze the unused parts whenever I make grilled chicken (no one in my family will eat backs or the parts of wings other than the drummettes, and both my wife and son prefer breast fillets rather than whole breasts). So, after cutting up the chicken I'll divide it in two two ziptop bags -- one to freeze and one to brine for grilling. Likewise, whenever we eat a supermarket "wonder-roast" chicken, I'll freeze the carcass from that as well after we've sliced off all the meat. This, combined with leftover produce and some herbs from our herb garden, is all you need to make stock.
So on to the recipe:
Basic chicken stock(Makes about 12-14 cups of stock)
1 or 2 chicken carcasses or equivalent chicken parts (particularly backs, rib bones, necks and wings)
3 carrots, coarsely chopped
3 stalks celery, coarsely chopped
1 leek, cleaned and coarsely chopped
1 onion, quartered
2 cloves garlic, crushed
20 whole peppercorns
2 bay leaves
1 bunch parsley (7 or 8 stems)
1 bunch fresh thyme (2 or three stems)
salt to taste
Place all ingredients in a large stock pot (ours is a 6 quart model, which is about the minimum for this) and fill with water until you've just covered the meat and vegetables. Place over medium heat until it just starts to boil, then immediately lower the heat down and simmer for 6-7 hours. Skim off any scum and fat that rises to the surface and also replace any water lost during the cooking process.
After simmering for 6-7 hours, strain through a colander lined with cheesecloth or paper towels into another stock pot or large bowl and submerge one gallon-sized ziptop bag filled with ice into the new container. Once the ice melts the stock should be cool enough to move into a refrigerator overnight. If you line the top of your container with plastic wrap so that the wrap touches the surface of the stock, then in the morning you will be able to lift off the wrap and most (if not all) of the fat that has separated from the stock will come up with the plastic wrap.
Divide into quart or smaller ziptop bags and freeze until needed. The resulting liquid love is shown below:

If you want smaller portions for use in sauces, freeze part of your stock in ice cube trays and then after they have frozen, place the stock cubes in ziptop bags in the freezer.