Every time I have a whole chicken that I plan to roast, I cut out the backbone, throw it in a ziploc bag, and freeze it for stock use. I do the same with wing tips when I'm making chicken wings, and whole chicken carcasses when I cut all of the meat off of a whole bird. Freezing these bones over time is a great way to get the most bang for your buck, and is also a great way to eliminate food waste.