Tire Sandals: Innovative footwear recycled from old tires.
...Innovative as of when? "Rubber tire sandals were used extensively by the Viet Minh and Viet Cong during the war in Vietnam from the late 1940's until the fall of Saigon in 1979."
Another detailed plan with photos.
Or if you're too lazy to make your own, and your dad or some American relative isn't going to disown you or haunt you for this, you could buy a pair from Old Ho's Rubber Tire Sandal Co.