I keep my caps that I have for trade in these plastic bins with compartments that I purchased from a walmart in the fishing department.
The compartments are labelled with little circular stickers and marked with the reference number given to that cap from my excel spreadsheet.
When I Receive new caps, I add them onto my excel spreadsheet. They are added with a reference number (The first 3 letters of the brand and numbers to follow), a picture, the brand and name of the cap, the amount of caps I have and the country of origin.
I work with color systems. Blue signifies I have only one of the cap, which is in my album for my personal collection.
Green signifies the cap has a double, which gets added to my plastic bins.
I also keep a spreadsheet for all the countries I acquire and a spreadsheet for caps that I want to add to my collection.
Caps that are added to my collection are added to my binders by brand and labelled for easy reference. The reference numbers are written in black sharpie behind the cap and are added into plastic coin sheets that I purchased from a specialty coin collecting store.