We use way too many plastic bags worldwide with complete disregard for the environment and the dangers it creates for animals.
All major supermarkets need to get together and agree to either:
1) Supply only "bag-for-life" bags and charge a set price to avoid price competition between eachother.
2) Charge customers for the use of single-use bags in order to deter use and encourage the re-using of bags (or purchasing of bags-for-life).
By doing this, I don't see how the supermarkets can possibly lose any money, and should in fact MAKE money. Supermarkets should spend more time promoting the sales of bags-for-life (e.g. by training staff to promote them).
Coming from the UK, this applies to Tesco, Sainsburys, ASDA, Morrisons, Marks and Spencers, Budgens, Co-op, waitrose and many more. However, this also applies to supermarkets worldwide, such as Wal-mart.
So please, take some time to support this cause and finally have something done about it!