I NEVER buy stock from the store. It's so easy to make at home. It is also a great way to really stretch your food dollar since you make stock from food you'd otherwise throw away. It does take a little work one day every few months and it takes a good bit of freezer space, both for storing the bones and veggie scraps and for storing the finished product. If you don't have an extra freezer, you can still make stock, you'll just want to do it more often.
Save every chicken bone, turkey bone, onion peel, carrot scraping, etc. in your freezer. I reuse ziptop gallon bags and keep one in my small freezer to dump all the scraps into. Once it's full, I have a special spot in my big freezer where all these get stored until stock making time. You can get started with just one bag full of scraps.
Throw your bones & veggie scraps into a pot. I have a large stock pot and will make 3 gallons at a time. Aim for the scraps to fill the pot to the top. Even if you can't get the lid on right away, it'll thaw and cook down quickly enough to get the lid on. If you're feeling adventurous, add some fresh or dried herbs. I don't usually add many herbs because I want to keep it pretty neutral so I can dress it up for different meal purposes. Some salt is also a nice addition though it can be added as you use the stock later. Chicken stock especially needs SOME salt to have any flavor.
Add water to almost but not entirely cover your bones and veggies. Bring to boil and turn down to simmer. Now, go knit a blanket, scrub your baseboards, read War & Peace... twice. Whatever will keep you busy for about 8 hours since that's the MINIMUM you want to cook this. The point is to give the bones plenty of time to give up their yummy collagen. The bones will fall apart with the slightest pressure once it's done. Its almost impossible to overcook it. I typically run my 3 gallon pot for 12 hours.
Now you need to strain all this goodness. The veggies and bones have given their all and are ready for the trash heap. I use a colander over a pitcher/bowl and a handled Pyrex measuring cup to scoop the stock into the colander and drain... throwing away the solids bits as you go. Let it cool some. If it's summer, I set the pot of strained stock down in a cooler with some ice. If it's winter, I use my "walk-out freezer" to cool it, tying down the lid on the pot and setting it outside for a bit. I store my stock in plastic baggies. My choice for freezer storage is Ziploc quart-size freezer bags. Use the quart size! I have given up on the gallon-size... too dang hard to thaw a slab that big. Fill your quart bag and make sure it's well sealed then lay flat to freeze. Once it's frozen flat, you can stack them flat, upright, whatever to fit them in your freezer... unless you plan to immediately use the stock then no Ziploc necessary. You can also use glass quart jars, just be sure to use wide mouth. Freezing liquids can break the shoulder on regular mouth jars... then you lose a batch of stock AND a canning jar.
When cool, this stock is nearly solid from the collagen and has the BEST flavor. You'll never go back to thin, boring grocery store stock after you make your own.