[kirklancaster]

The best way to upset these greedy bastards, is to make sure you take a rival supermarket's bags - printed with their name and logo - with you, then at the check out when you're asked if you need bags, ask if they're charged for. If they say 'yes', ask them why you should be charged for carrying their advertising around for them. You will not get any valid answer, but you will get pissed off looks when you say 'No thank you then' and proceed to pack their products in a rival's carriers.

I've done it many times, and believe me it really pisses them off.