The Indiana Election Division sends its notices out with a small styrofoam cube in the envelope; the cube increases the envelope's thickness to 3/4", so it qualifies for discounted parcel-rate shipping.
The Styrofoam cube enclosed in this envelope is being included by the sender to meet a United States Postal Service regulation. This regulation requires a first class letter or flat using the Delivery or Signature Confirmation service to become a parcel and that it "is in a box or, if not in a box, is more than 3/4 of an inch thick at its thickest point." The cube has no other purpose and may be disposed of upon opening this correspondence.
The Styrofoam Cube In This Letter Serves A Bureaucratic Purpose [consumerist.com]
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.