There are tons of patterns for bags on the web, but the Booga Bag seems to be a favorite.
http://www.blacksheepbags.com/booga_bag.html
www.knittingpatterncentral.com or
www.ravelry.com are both good places for patterns, though the first has only patterns and is easier to navigate for that purpose.
As for cast-off, check out the videos at the top of the page.