It's always fun to make themed plastic bag bags - for holidays, special events, or sports teams.
For example, steelers fans are a really enthusiastic bunch - and my grandma, who lives in Pittsburgh, Pennsylvania is one of them. I crocheted her this plastic bag Steelers bag for her birthday. She takes it with her every time she goes to the Giant Eagle grocery shore and she always gets tons of compliments!
I recently spent some time traveling around Iceland. And while I was there, I ended up teaching a plastic bag crochet workshop in Reykjavik. Some of the girls at the meeting were part of an organization called Green Drinks. I'm not too familiar with it, but it sounds pretty cool.