Surplus has always been used as it was intended for or, as this example shows, altered to fit the needs of the individual. 

Here is a pair of WW2 US medic bags that at some point, the D-rings were cut off and extra straps were added to the back. These straps can be attached together and worn together or used as saddle bags. Other than that, the bags are in good shape, but they have some stains and storage wear. 
 
Only one pair available.