http://www.morsbags.com/ [1] has a great downloadable tutorial for making your own reusable grocery sacks.

[1]
"let’s do something positive to reduce the hideous number of plastic bags being used - 1 million are consumed per minute globally - of which hundreds of thousands end up in the oceans.

the idea is to get together with people in your local community, drink wine and make reusable cloth bags (from old duvet covers, curtains from charity shops etc) and hand them out to the unsuspecting public for free on specified dates outside different supermarkets." - from their website.

http://www.flickr.com/groups/morsbags/ [2] - their flickr group