I subscribe to the "odds and ends" version of making chicken and vegetable stock.
I have a couple of plastic bags in the freezer. One I toss chicken bones (when deboning thighs) / wing tips / carcasses of roasted chickens into, the other, I toss veggie ends into - the woody parts of asparagus, carrot peels, broccoli stems, etc. When the bags get large enough, I make stock - which I cool and then freeze in small containers for later use. The addition of herbs comes later in what ever soup / stew I am cooking that the stock goes into.
I have bags of pacific crawfish and black tiger prawn heads and shells in the freezer for use in making stock later used for bisques or sauces. I think using a pressure cooker on these would be a great idea!