It is remarkable how readily plastic bags are given out here, by pretty well all shops. I bought a sealed bag of dry catfood recently, and before I knew what was happening it had been put into another plastic bag. Since they're all imported the best thing is for a substantial import levy on them, so that they cost the shops a lot to give out and they have to charge for them. I suggest 50c for each bag. That's the only way their use will be curtailed.
To be fair, in England paper bags have returned to being widespread, but they're useless when they get wet. So paper bags would be unusable here for many months of the year.
The only solution is to take your own durable bag, probably based on canvas. Or be prepared to pay for a plastic one.