Here's a great money-saving idea for you -- T-shirt bags!
T-shirt bags are a bit more green than frugal but the wonderful thing about being frugal is that it is green most of the time!
I ran across these super easy directions for making T-shirt bags and just had to try it. All you do is turn the shirt wrong side out, sew up the bottom hem, cut off the sleeves and cut a scoop out of the neck and you're done!
These bags can be used for literally anything! I have these three big ones in the picture here. The green one currently contains diapering supplies that aren't used on a daily basis. The white one most recently held little girls' clothes for an overnight visit at their cousins' house. The Winnie the Pooh bag (does anyone recognize this shirt?) is also for diaper/baby stuff since I have an official diaper bag with Winnie the Pooh on it.
My girls have several small bags, most of which my older daughter and her cousin made out of some of their own old T-shirts. Their collection of T-shirt bags consists mostly of purses and baby bags.
I keep intending to make several medium sized ones for using at the store since I do not need one more plastic bag in my house. (We are being overrun with the things.) I keep forgetting to make the bags, though, but once I ever remember I'm going to stash them in the car so they'll be there when I need them.