A project that doesn't cost anything AND makes the kitchen look neater??

Yep. All you need is a kitchen dishrag. (I think I may be starting to sound like a telemarketer. I will try to resolve that). Follow the instructions here.
 

I changed it slightly-- I used an old worn-out hair-tie for the elastic and cut it a little shorter to use some of the fabric for the strap since I didn't have any fancy twill tape on hand. Oh, and I used a button in my case because I wanted to loop it over the side bar of our table.

It looks a little lumpy because we don't actually have that many plastic bags right now... But that's a good thing right? We typically use reusable bags we brought back from France when we remember to take them with us. My family even sent us some with pictures of my hometown on them... talk about grocery shopping in style! :)