Whenever I go to the grocery stores, I try to check how many people are using reusable bags. According to my observation, the ratio is 1 to 30 at the local grocery stores. At Trader Joe's or Whole Foods, it is 1 to 10. It is my observation at where I live, so it's not a representative sample.
But in anyways, it's far below 20% or 50% participation rate.
What can be done to increase the participation then?
How about a little incentive? Japanese shops love this mileage-like system called "point-card" or "stamp-card". It is a credit card sized card that you can put in your purse. Whenever customers purchase something, they get a point or a stamp on it. When the card gets full, the customers get credits. (maybe $5 worth). It's not much. But this has been a widely used marketing program just to increase the loyal customers that visit the shop on a regular basis.
These days, a lot of Japanese grocery stores use this card as an incentive for using reusable bags. On the other hand, I recently noticed that the grocery store in my town started to give 5 cents discount for reusable bag users. The idea is completely the same.
However, if you are a store owner concerned with the expense for incentivizing cusotmers, you might choose stamp-card because you'd only reimburse to the loyal customers who purchase at your place so many times!
I am not advocating minimizing expense for environmental causes though. My point here is that even reluctant business owners can begin this just as a marketing program, thus reaching much wider public for participation.