For the past decade, I've been a plastic grocery bag hoarder specifically for the purpose of picking up my dog's poop. She's gone, now, but for 10 years, we used at least two bags/day.
I'm convinced that I was on a "watch list," at my local grocery store because they always insisted that they bag for me. I would usually bag my own and use way more bags than I needed.
When I used the Walmart self-checkout, I would double bag every single bag. Sometimes triple bag. I've probably got 200+ of those *****. We still use them to scoop out the cats' litter boxes.
I think the ban is silly, but I really don't care about it (especially since I no longer have a dog). That NPR link that WikiEII posted above shows how silly it is.
I wonder if it would be okay for me to bring the plastic bags I've collected to the grocery store and ask them to use those.