I begin this process every Monday, everything I would normally throw away, the vegetable peelings, vegetable ends, even onion peelings, I wash them and store in the freezer (in a freezer bag) all week long. When Sunday rolls around I make vegetable stock, if I am busy on a Sunday I just carry it over till the next week and make a double batch. This is very economical (because its more or less free) and whats left over after making stock, I give to the chickens. When done I store the broth in freezer bags, we tend to use the broth before two months are up, but it would probably keep in the freezer a little longer.
I also do this with chicken bones, ham bones etc..I just make the broth, label, date and store in freezer and then its ready when I need it, quick, easy and cheep!