Commonly associated with troops during Operation Desert Storm, these bags were used from 1959 until the mid-1990s. They have been used in the Vietnam War and the Gulf War, with minor changes occurring throughout the years.
 
Made of heavy canvas, it is durable and great for hiking or even bike riding! (I used it on my bike to carry a 3.5-pound bag of cat food and worked surprisingly well). 

There is an extra strap that would go around your waist or leg to prevent the bag from flopping around.