I am going to model industries that actually were here in Ft Wayne in 1900. My primary industry is a grocer’s warehouse.
IN
reefers - meat, dairy, vegetables
ventilated boxcar - fruits, vegetables
boxcar - soap, office supplies, paper bags
OUT
all empty
Another industry is a meat packing plant. Of course, some of the meat goes across town in reefers.
Sometimes a gondola full of [CENSORED] goes from the meat packer to Bash Fertilizer. Bash brings in any kind of car you want and ships out tank cars, boxcars loaded with fertilizers.
A soap factory brings in boxcars full of … umm, what IS soap made of? … and boxes and wrappers. Also tank cars carrying lye. The boxcars leave carrying crates of packaged soap. The tank cars leave empty. Sometimes a loaded boxcar goes across town.
An asphalt plant brings in tank cars full of petrol and sends out tank cars full of asphalt (maybe not the same tank cars, need to do more research on that).
The interurbans they are a’ building! Construction supplies, road-fixing stuff (bricks, cobblestones), ballast, ties, rails come in by boxcar and gondola. Occasionally a new electric car comes in by flatcar. Scraps go out, probably by gondola.
General Electric brings in motor parts by boxcar, empties them and reloads the car with motors and light bulbs and such. Sometimes a flatcar is required for big motors.
Steel Dredge builds, well, dredges and steam shovels and such. They bring in parts by boxcar and ship out whole dredges by flatcar.
Aichele Monuments brings in big chunks of stone by flatcar or gondola and ships out empties.
I have tried to ‘chain’ some of the industries together so a given car can float around the layout and earn revenue before disappearing off the interchange track. Sometimes it works!