A couple of months ago I wrote an article on paper bags vs plastic bags. The general conclusion was that both were almost as bad as each other. Plastic did edge out paper by a small margin, but this all depends on how you measure it.
MSNC has created a cool little website called Battle of the Bags: Paper vs Plastic. This is an interactive website providing a great overview of the issue. Again, the general consensus is that paper and plastic are just as bad as each other and it’s much better to get yourself a reusable bag. But the site does provide some useful tips for those occasions when you forget your reusable bag.