Covering old food containers with concrete to use as planters. Given the wide variety of shapes things come in, you could have a lot of fun with this. Top it off with textured stone spray paint, and you have a really cool "rock" planter for all your earthy design needs.
I decided to make my own solar powered garden lights using things found at the Dollar Tree. I stumbled upon the cut glass jars in the cosmetic section and was happy to find the solar garden stakes fit on top perfectly. I though the pattern on the jars would give off pretty reflection on the trees. They remind me of vintage salt and pepper shakers.