Cover an empty juice box's straw hole with tape.
Cut a 4" high by 3" wide triangular sail from a Tyvek envelope (I used an old USPS Priority Mail envelope).
Decorate the sail with colored tape and make a little flag. Have fun and add a monogram or number to mark the sail.
Push a small wooden skewer through both sides of the box so that it sticks out underneath about an inch or so.
Use tape to attach your sail to the skewer leaving about 1/3" of space at the top.
Above the sail attach the flag.