...I just got trained up on always having a few cloth bags in the trunk...
And there's the rub. You can easily carry reusable bags with you in your car pretty much all the time. I don't own a car, and always walk to make most of my purchases. I am pretty sure this results in a smaller carbon footprint. Nevertheless, I am expected to carry reusable bags with me at all times. This one-size-fits-all approach to environmentalism is a crock.