We have also trained ourselves to keep cloth bags in our vehicles. When we go to the grocery store, we take the bags in to be used for sacking our groceries.
We don't always take the cloth bags into stores like Target or the drug store, but we often walk out of those stores carrying our purchases sans disposable bag.
It's amazing how this change in behavior has reduced the number of paper and plastic sacks that come into our home!
How do you bring your groceries (or other purchases) home? In a plastic or paper sack? If yes, can you make a small change in your routine and keep cloth bags in your vehicle to use when shopping?
You'd be amazed at how quickly you will become accustomed to taking in your own bags to a store. I promise!