Everything is in documents in my computer.
The main category is train sets. Sets are broken down by manufacturer and then by relative categories (postwar Lionel, prewar Lionel and LTI Lionel, for example). Within each set, I have an inventory, log (containing history of the set) and expanded inventory (greater detail for each piece).
I further cross reference each item in the sets by locomotives, freight cars, etc. in another setting.
I also keep an inventory based on location in containers, and by where sets are stored (the reverse) in still another setting.
I avoid duplicate purchases. I know where everything is and I can find it.
I also can review why I purchased an item, so that years later, I can remember why I did what I did.
I also have individual photos of each piece scanned into the inventory.
I enjoy adding to my collection and find it relaxing to blend new items into the over-all picture to determine what the trends are.
I also have a camcorder to document the sets. I have a carpet cental at Christmas and have a permanent layout. So, if I ever become disabled, I will be able to click on my trains and still enjoy them.
My ancestors would have said: "Wir mussen Ordnung sein". There must be order.
Best,
Mark