Are you kidding? There are non useable parts?
Seriously, the feet make the absolute BEST chicken stock you will EVER find. What I do is blanch the feet for 1-2 minutes in boiling water so that the skin peels off. Its just like pulling off a sock at that point. Once the skin is off, I add them to a pot of boiling water, with a few carrots and celery and simmer for an hour or so. Cool and pour into jars to freeze or refrigerate. I kid you not - it will be hard to go back to regular chicken stock after you've tried this.
The heads - I do the same, except for the blanching part.
For both feet and heads, after they've simmered, I give the remainder to the pets. The dogs get the feet. The chickens get the heads
The insides? Well, it depends if you are talking organ meat or intestines. The first time I processed, I cooked up the intestines and fed to the dogs. They didn't mind, but the smell was pretty rank so last time I tossed them. I'd be willing to cook them up on an outside burner though, if I had one. The organ meats can be eaten - either by people or pets. The gonads are a delicacy (ever hear of rocky mountain oysters?) while both the chickens and the dogs will be happy to eat liver, kidneys, heart, brain etc.
The gizzard is actually a delicacy, a pricey dish in fancy restaurants. Google how to cook it in a sauce that makes it zing. Yum!
The ONLY part of the chicken I threw away was the feathers. And I even felt guilty about that, thinking I should dry them out and make a pillow or quill or something.