Have you looked up the pillowcase bag(I think that is the name of it ) ? That one is super simple, basically cut to size, then cut out the handles-sew it up, put bias around the handles and you have a bag.
http://spiderwomanknits.typepad.com/...-tutorial.html
http://growmama.blogspot.com/2010/10...illowcase.html
Here ya go if you are looking for a shopping bag- I am sure it could be modified for a purse like bag. Try Ikat (I believe is the name of the blog). She has some great instructions for bags, purses.
http://www.ikatbag.com/