I haven't tried this but I surely will !
Organic Vegetable Stock
You don’t need to buy any extra vegetables to make your own vegetable stock (salt free if you like!) - just keep the peels when you peel potatoes, carrots, onions, etc in a zip tight freezer bag, since it's frozen you are in no rush to use them.
Add about 4 cups of peels to a generous amount of water, season with salt, pepper and any herbs you like (you can use the slow cooker for this). Let it simmer for a while, and you will have great organic stock without needing to buy anything extra vegetables and re-using the peels from the ones you use.