In 1985 I was asked by a hardware store owner whether it was still possible to receive bagged coal in boxcars.  The market was home heating.  I didn't know and made calls to find out.  The answer was, "Not any more."  I did learn that back in the era covered by this list, it was common.  I talked to a company in Duluth which had bought coal by the ore boat load and had a bagging line.  "We finally scrapped that machinery a couple of years ago."  Boxcar grain from the prairies was trans-shipped into boats at Duluth.  Some of the boxcars returned to the prairies loaded with bagged coal bought by grain elevators who also sold coal.  I don't know what the percentage of loads both ways was.
Alex Huff, retired South Dakota railroader & S scale modeler