This is my 3 yr old son, Owen as a box of McDonald's French fries. My niece went as a hamburger (bought online) but we couldn't find a fry costume so I decided to make one.
I started this Homemade French Fry Costume with a medium sized box with a hole cut in the bottom big enough for his legs to fit through. I taped the flaps on the top of the box together so they would stay up. I then cut U shapes around all four sides, the front and back are for the shape of a usual fry box and the two on the side are for his arms. I then took two pieces of cardboard (from another box) and taped them inside the box about 6-8" from the top, this was like a table inside the box for the fries to sit on but I left enough room for his body inside the box.
I spray painted the entire box with red paint (I recommend using an expensive brand). I bought a pack of Styrofoam insulation sheets at Lowes (pk of 7 for around 7 bucks) and cut the whole stack into the "fries" (measuring approx. 14" tall and 2.5" wide), this gave me roughly 20 fries. I then spray painted each one yellow (again, I highly recommend using an expensive paint).
I hot glued each fry into the corner of the box. Once they were in the box I misted the tops of them with a brown spray paint to give them a golden cooked finish. I bought a yellow wooden M at Walmart in the craft section and cut the sharp corners off the top so it would look like the "arches". I glued one to the front and back. I purchased wide red ribbon to make the straps to hold it up and punched holes in the cardboard the fries are glued to and tied knots underneath. The ribbon went over his shoulders like suspenders.
I received tons of compliments while Trick or Treating and it even scored him a free ice cream cone from McDonalds!