I have two of these. They're reusable shopping bags that roll up into a built-in pouch. But with the sort of design and quality you'd probably expect from Peak Design.
They could definitely fold/scrunch up smaller, but that would make it take longer to do. I've had a similar bag that was much smaller to carry, but it took at least a couple of minutes to pack it away - these can be done in maybe ten seconds.
They're strong. The handle is comfortable. They have a zip, so your shopping doesn't get wet if it's raining. I live in Devon, it's probably raining.
I almost always have one in my bag (Wandrd Rogue 6l Sling), and if I don't have one, it's most likely because I have two.