For those who are in Facebook, there is a campaign called "Say No to plastic bags on 1 May 2008. No attendance necessary, just don't accept any plastic bags in shops on 1 May". Hope it doesn't stop but it becomes a lifestyle.
There are many alternative bags or containers we can use to carry stuff we buy. I remember in a supermarket in Wageningen, The Netherlands, no plastic bags are given. You either have to bring your own bag, or you can use the empty boxes/cartons the shop provides near the counter. I think this is one way shops can also participate in this campaign.
In our campus here at AIT, at least now they have a campaign also to use less plastic. Maybe this time people here are more receptive. Because many years before in the early 90s a group also campaigned for this here on campus and even the green grocer was willing to follow. But the owner said that the customers themselves would demand for plastic bags, so what could she do? That was before, and it seems things are getting better. At least there is a memo from the top to all the shops so hopefully everyone complies.