Random Number Generator
Some of the different operation methods require a "random number generator". There are a number of ways to do that - Spreadsheet formula, sheets of paper pulled from a hat, using dice, using a deck of cards, etc.
Personally, I have created a card for each of my train cars, a "Car Card" if you will. These cards are not the "card with a pocket" most people think of when they hear "car card" but more like a baseball card/trading card. Then when I need to do something random, I use the cards. If I need to pick 10 random pieces of rolling stock, I spread them all out face down, and pick out 10 cards. If I need to assign my 10 cars to 3 random locations, I pick out the ten cards needs, shuffle them up, and then "deal" the out to three stacks.
See more about how I made and how I use my Car Cards
The benefit to me is that:
In N-Scale, the road number/reporting marks can be pretty small, so the photo reference is a big help.
The same cards can be used in a "Car Cards & Waybills" operation .
As seen on "DIY and Digital Railroad" https://www.youtube.com/watch?v=5MVCA0kAgKQ. I suggest you watch the video for full details, but my summary is:
Check how many industries you have on the layout (include the yard if you have one), and how many cars can be held at each industry. This will give you a MAXIMUM number of rolling stock you can use.
Pick out the rolling stock you want to use, and list them on a sheet of paper/spreadsheet/etc.
Assign each industry a number starting at 1.
Go down your list of rolling stock, and using a random number generator set to number of industries, assign each car a starting location. (If you exceed the industry limit, then just generate another random number. )
Now repeat step 4 to get a finishing location for each piece of rolling stock.
Car Cards & Waybills
Presentation I found about CC&WB -- https://www.tulsanmra.org/resources/DRS_CardCards.pdf
Three part article from trains.com:
See my CC&WB setup -- Car Cards