Making up prototypical consists for you trains is fun. I suggest you refer to you tube videos and books on real life railroads for examples of which cars will fit your engine's railroad. The era you are trying model does figure into you choices.
I model mostly the Erie-Lackawanna Railroad and its predecessors. I try to include freight cars that I have seen on this railroad in publications and from memories of trains that I recall from my youth. So, for example, there are Pittsburg and Shawmut coal hoppers on my E-L trains. I also have Canadian Pacific "PACMAN" box cars hauling newsprint. The E-L had many connections in the northeast so almost any eastern box car can show up in my trains. Refrigerator cars bringing produce can come from as far away as California so western road names can show up too. Even passenger operations can show some variety. I like to add a Nickle Plate coach, sleeper, or baggage/express car to my E-L consists as they appeared years ago on the mainline where I live. A visiting business car from the D&H (Well, the president of the road brought it with him) may bring up the markers.
When running these consists on our club's modular layout it makes for good conversation. Do some research and have some fun.
Earl
