Milk sales have doubled at McDonald's since the launch last year of single-serve, plastic, re-closeable bottles. Wendy's has had similar success. Neither restaurant has done it on the cheap. Milk in a paper carton was selling for about 89 cents per half pint; in the plastic, half-pint bottles, milk is selling for as much as $1.19. It is not a commodity. As I write this, Burger King has just completed a two-month long test of plastic bottles. By the time you read this, the folks at BK, the third largest quick-service burger chain, may have already announced a national roll-out for early 2006.