Reusable supermarket bags are environmentally friendly, but only if you actually use them, many times. And you're probably not using the crappy "reusable" bags you got from your local Coles or Woolworths, which sit in your kitchen cabinet until you eventually throw them out.
Meanwhile, you end up out somewhere and suddenly need a bag. Your purse or backpack is already carrying whatever it usually carries. So you use like five disposable plastic bags and you feel like a schmuck and your hands hurt.
You need a better bag. A big bag that can hold almost anything, whether it's bulky, fragile, or wet. And you need to have it on you at all times.
Buy the Right Bag
You'll only use a bag you actually like. And you'll like your bag if it's:
Compact: Small enough to shove in your pocket.
Comfortable: With a long handle you can sling over your shoulder.
Self-contained: Rolls up into itself or a built-in little holder bag.
Big and strong: Can carry a heavy load of library books or groceries.
Pretty: Not embarrassing to carry.
Whatever you get, pay attention to the size. Get a big one. Because they don't hold much of a shape, there's not much downside to a bigger bag.
Avoid canvas totes, which are heavy and bulky. I mean, if you want to carry a bundle of canvas totes to the greenmarket, good on you. But they're terrible "carry everywhere" bags.
For the last month, much of Australia has been gripped in an insane tempest of petulance and stupidity because single-use plastic bags aren't available in supermarkets any more. This is so first-world problems it's almost as embarrassing as our national energy policy, but for anyone who is still stressing about this, I'm here to tell you IKEA can save you.
Take It Everywhere
Because you really never know when you'll need more storage space, especially if you're going without a car. Keep your everywhere bag in your coat pocket, your backpack, or your purse. Carrying a bag in a bag might feel awkward, but it's way less awkward than carrying stuff in your arms.
A sometimes bag is almost as useless as no bag. You'll end up getting a disposable bag from the store, or carrying a pile of stuff in your arms and you'll have wasted your money and carbon footprint on an extra piece of nylon trash.
The greatest thing about these bags is that you can get them filthy and just wash them out in the sink. And you really need to wash them if you're carrying food in them. Get two, so you can take one out while the other air-dries. (It's OK, again, so long as you're really using them.)
Don't Take Free Bags
Don't accept free bags from organisations and companies. They're always bulky and ugly and cheaply made, so you won't end up using them. Whenever you can, discourage the handing out of these unwanted bags, which are making the environment worse.
Of course, you will get stuck with these bad bags against your will. One charity mailed one to me, which is shameful. Put all your Salvos donations in them, so you can drop the bag right off.