Put the leftover bones, the chicken back (chopped into smaller pieces), wings, and skin from a chicken carcass into a large stock pot and cover with cold water. Add vegetables like celery, onion, carrots, parsley. I usually make stock at the end of the week and use any veggies that are going to go back soon. Use all of the vegetables including the greens and stems.
Add about a teaspoon of salt (or more to taste) and a teaspoon of pepper.
Bring this to a boil, and once it starts to boil, reduce to medium heat.
Simmer uncovered at 4-5 hours, occasionally skimming off the fat that comes to the surface, and adding more water if necessary. After 4-5 hours remove the bones and strain the stock. If you want to make it more concentrated for storage let it simmer uncovered a few more hours. You can store stock in the refrigerator for up to a week and frozen for several months.