I user a piece of track in Surveyor like Cascade Railroad does to configure a bunch-o-consists ahead of time. I'll gather various boxcars together, then tanks, hoppers, flats, etc. then cut the giant consist apart. I'll then save the individual consists and name them based on the number and type of cars in the consist. Let's say I have 20 box cars, I'll call this consist 20x ---- Boxcars.
Once I have these consists, I then mix and match cars from them to make up some mixed freight consists of various lengths. I call these Mixed Freight Long ---- 01, Mixed Freight Long ---- 02, and repeat this with various configurations. I also do this with smaller consists and consists of engines only, passenger trains, trolley cars, subways, etc.
With these consists, I can then add them to portal trains, other trains, use them as yard components, and when I've run out of cars during a session, I can then add them back in somewhere using the quick drive as needed.
John