Vegetable Stock can be made or purchased in a prepared carton and powder, it is basically just vegetable and herb infused water.
I always use an organic low-sodium stock like Pacific Natural Foods. Look at the ingredients list, it should be made up of vegetables, herbs and sea salt, anything else is just added crap you don’t need!
For a instant powder mix, chose carefully, I have a box I picked up from Whole Foods: Gayelord Hauser Instant All Natural Vegetable Broth. I like this one because it has a special high potency, non-active nutritional yeast (grown in beet molasses) plus a whole list of healthy ingredients – NO ADDED CRAP!