Model ‘removable’ loads. When I get my layout up and running, I’m going to incur basicaly the same problem as you but with a coal mine. Prototypically, most loads won’t get emptied the same day they’re delivered, so the problem is easy to deal with by emptying the car after the session. In your scenario of an open gondola with a scrap load, they may start working on unloading it asap, but it’ll still take them a while, and by that time, they probably won’t have called the RR back to schedule the pickup of the empty car.
The way I solve this problem is, after you’ve delivered the car, at the end of the operating session, simply pick the car up by hand, remove the load, and replace the car on the layout. For instance, with scrap metal, one easy way to model it is with crumpled bits of aluminum foil, browned in the oven or painted to resemble scrap metal. When your car is loaded, dump a handful of the aluminum foil pieces in the car and set it on your layout wherever it’s staged or loaded first. When the car is delivered to it’s unloading destination, dump out the foil and replace the car on the layout.
Some model manufacturers even offer one piece ‘open car loads’ to go with their hoppers and gondolas. That way, you simply slide the load in place, deliver the car, and pull out the load when the car is supposed to be picked up empty. For instance, Walther’s offers coal, aggregate, and container loads for their hoppers and gondola’s. Alot easier than dealing with dumping out an whole carful of loose coal, ballast, gravel, scrap metal, etc each time you need to empty the car, not to mention the mess loose loads would make if they derailed and toppled the car.
Also, check out the article in the Feb MRR (p.40) regarding the waybills and car cards for starting your operations paperwork. MicroMark sells the preprinted waybills, car cards, locomotive cards, and bad order slips, plus the card boxes for a very reasonable price if you don’t want to bother with printing you