To wear (*after* cutting arm and head openings -- and, no, you don't step *into* it, you put if over your head. On the other hand, *don't* cut the holes) to the starting line as a wind breaker (and moisture retainer so you can freeze once you take it off). Other uses: something to blow into the Potomac or decorate trees when you toss it; something to choke local fauna and small children; something to serve as a body tent while you squat to pee while in the middle of thousands of other runners (women only; men have trees, walls, and other runners); temporary body bag.