Here's my mixed train on my son's war layout. I know that the mixed trains on the Clinton Sub used the old six axle heavyweight baggage cars most of the time, and they had a wooden caboose, but this is the general idea of what it looked like.
Here's my mixed train again! The two boxcars, and the small brown hopper have been weathered. I bought the yellow boxcar already weathered, while the brown boxcar and brown hopper have been weathered by me. the black Burlington hopper was painted and lettered by me as well.