What is your environmental passion?

What do you do if you find yourself in the situation of needing a bag for items but don't have a reusable one with you? Carry things out in your hands? In a cart? Accept a disposable one? If you find yourself in this position often, what system could you put in place to try to create a successful habit of not using plastic bags?

What environmentally friendly habit have you most recently implemented? How do you ensure that you are successful in creating or changing a habit?