How many times have you gone to the supermarket for just one or two things, only to go home with more products than planned. Of course you didn't bring a jute bag with you because you only needed to buy a few ingredients. This happens relatively often. The options are then:
A: carrying everything home in a pile in your arms, right
B: buying a paper bag, which often tears on the way home and has to be thrown away immediately.
Such situations are annoying, but the good thing is, they can easily be avoided with a little pre-planning and self-discipline.
Try carrying a small shopping bag in every bag. This doesn't take up a lot of space, nor is it particularly heavy.
If you are a fan of coffee to go, take a reusable coffee cup with you. Cafés often also offer reusable cups that can be rented for a small deposit.
It's a small step, but it already has a big impact.