I'm absolutely flabbergasted at how effectively the supermarkets in my town changed behavior by charging for bags. Of course, it helps that they're a cartel: if any store in this neighborhood hadn't adopted the "5 yen per bag OR bring your own" on the same day, they would have done quite a bit of business.

I even bought myself a shopping bag, even though my math brain told me that I would likely have to live in Japan for at least another six years until I had recouped the $9 it cost me.