I have just got back from my local tesco metro and was extremely annoyed by the three people in front of me, one bought a loaf of bread and a pint of milk, another a newspaper and a loaf of bread, and the third a bottle of water and a sandwich (wonder if her 'healthy lunch had aspartame in it?).
ALL 3 customers put their purchases in a plastic bag, and two of them then got in their car.
Surely we should only be using carrier bags when our hands are full?
I used to work in a bakery and was amazed by how many people wanted a bag for a small cake and a roll, so much so I started refusing regular lunchtime customers carrier bags with less than four items and when three or four people came in from the same office I'd let them have one bag between them.
I'm known for getting a bee in my bonnet but I really don't think laziness constitutes the damage plastic bags actually do.
Carrier bags should be for use if you have no other way to carry something, and then reused when possible. (Actually reuse them though, rather than collect them in the cupboards like I do!!)