It depends... if you have an overabundance of something, can get something really cheap/free, then it's definitely worth it to can it. But the problem is that many things (like tomatoes) require a pressure canner, which isn't a cheap purchase. If you can borrow one, that's great - or if you do a lot of it, eventually it'll pay for itself.
You can find canning jars in thrift stores, freecycle, ask everyone you know. I can buy yogurt and CO in reusable jars, which helps with the jar stash, but I still have to buy some every year.
Without a pressure canner, you're limited in what you can can... jams and pickles definitely, applesauce, fruits in syrup, that kind of thing.