Flip flops are the ultimate representation of summer's relaxation. Maybe shoot your favorite pair. Or show how many gather by the door on any given day. Or maybe shoot down if your standing, or long if your lying down.
Shoot directly, or gather the radiance on a long summer's eve. Withering plants, jugs of lemonade, tanned skin, or other effects of a strong summer sun also will fit!
Don't forget to save your photos to a separate file that you can access easily at the end of summer. And try to build as we go! It will make our project much more fun when summer's end comes!