If you're cooking with lots of veggies, you have the fixings for stock. As you cook throughout the week (or weeks), save the tops and peels in containers that you put into the freezer. Be sure to wash your vegetables before peeling or cutting the ends, as you don't want to end up with dirt in your stock.
I save scraps from carrots, onions (not the papery skins though), leeks, mushrooms, daikon radishes, potatoes, turnips, cabbage, butternut squash, parsnips, and celery -- but I don't save scraps from beets (it'll make for a very red stock, which then colors everything you make with it -- if you don't mind the color, save your beet scraps), radishes (except for daikon), or garlic (I think it would make the stock too pungent -- I want the stock to be fairly mild, so that I can flavor the dishes that I'm making with it).
Here's a container after preparing some daikon radishes and carrots.
I keep the tops of the carrots to give to our rabbit.
When you're done with your veggie prep, cover the container and put it into your freezer. If the container isn't full, you can just add on top of the frozen scraps the next time you prep veggies. If it's full, start another one.
Once I have a few containers, I'll make some stock. Next time I make it (still have some in the fridge from my last batch), I'll write a post showing how to do it.