Here in ROussillon. Since many stores do not stock grocery bags, customers take in their own. I have noticed, those who take in things like sacks from other stores, the security will seal them in banded plastic bags and then allow the customer to take in whatever.
Also, being on a bike sort of complicates things. I see people walking in the streets , on city buses , returning from work, school. That means if they use backpacks, they can't go shopping.