It is interesting to see box cars from western and mid-western railroads like Rock Island and Missouri Pacific (as International & Great Northern) spotted by the freight house in the early photo of the freight house. I wonder what their loads would have been.

It is. Those cars are at an "Out bound" freight house being loaded and sent back home.
Philadelphia in those days was known as "The Workshop of the World" they manufactured many things in particular textile goods, rugs, linoleum flooring, etc. Don't forget Brill, Baldwin, Midvale Steel, Budd, Hayes, Campbells, Heinze, Nabisco etc.
My bet is that those cars brought food stuffs like canned goods, grain, hops for breweries and machine tools.
The Midwest has long been a major producer of these. Especially the lathes, milling machines, and manufacturing equipment.
What strikes me as well is how busy this facility is.
As well this was where the ocean going ships to Europe were docked. So a midwesterm boxcar might have brought items for export. This facility was a large team track and freight house so I do not think they unloaded here for ships. That would be done in the dock warehouses and cars positioned on lighters for loading and unloading.

This morning's newspaper had a story about extensive lead mining along the area just west of the Mississippi River in Missouri. The I&GN car could have carried pig lead for some manufacturing purpose. Anyhow, to model this facility gives an excuse (er, explanation ) for non-RDG reporting marks among the models.

Learning how to post pictures

This is my modeling effort of this area. You are looking north and the Frankford El will be modeled behind the Freight House. The orginal could handle 20 or more cars, mine is a little shorter.
Looks like the photo upload is working. PTL.
Chris

It looks great, Chris! Keep us abreast of your progress.