Vegetable stock is super-easy to make, a great use for veggies that you can’t use otherwise, and it freezes really well. There’s no reason to spend money on watery broth with less flavor and very little nutritional content when you can make your own with only a few minutes’ effort and save it for future use.
I made a batch last weekend with carrots, chard stems, onions, garlic, mushrooms, and scallions.*
* I’m sure I’m forgetting a couple of things I threw in there, but that was basically it.
Mushrooms are great to add depth of flavor, but everything is pretty much optional and based on what veggies you have left over. I always use an onion (just quarter it — no need to chop) and usually carrots, but other than that, anything goes. Cabbage and other gas-producing vegetables (broccoli, cauliflower, and others) aren’t a great idea, but that leaves a ton of options.
Just chop up your veggies, throw it all in a big stock pot filled with water, bring to a boil, and simmer for 30 minutes or so. Salt it (if you like), cool slightly, and then store in labeled Ziploc freezer bags. I like to store mine mostly in 1 cup portions, so I can defrost just how much I need. If I have a lot, I’ll throw in a 4-cup portion or two, for making risotto, soups, and other stock-heavy dishes.