Ideally I like to make my own stock because it's less salty than bullion and it's way cheaper than the stuff you get in cans or aseptic container. If I just take them time it's really not all that hard.
I keep a bag of leftover veggies scraps from meals in the freezer. When that gets full I put it all in a pot with anything else I have on hand, fill the pot up with water...
Here's a basic recipe and how to if you are a stock virgin. Inspired from New Recipes from Moosewood.
2 large unpeeled potatoes and quartered
2 large carrots, peeled and sliced thickly
1 large onion and quartered
1 celery stock chopped
1 apple or pear seeded and quartered
1 bay leaf
10 cups water about 2.5 quarts
For a spicier stock add garlic cloves skins and all and a small amount of tomato. I always add garlic. I also will toss in onion peels and not always peel the other veggies I add. I always wash everything well.
Bring to a boil and simmer for about an hour. Strain the veggies out and put them in the compost if you have one. Then you are ready to use the stock or put in the fridge for the next day. If you don’t think you will be able to use it right away you can store in the freezer. Some can be put in ice cube trays so you can use a few cubes when you are cooking up some rice. After they are frozen place in a plastic bag.
You can measure out larger amounts and put it in a Rubbermaid container then after it freezes transfer it to plastic bags so you can have the container back.
If you want a chicken stock just save up your bones and skins as well in the freezer and add them to the veggies.