I basically store my (old) stuff in categories like kit, elements, alpha & so on. The new stuff I have sorted by stores. In my file for Oscraps (where I CT), I have everything sorted by designers. Then I have one file named CT Kits, where I download the new stuff I get. In that file I have a subfile named "Used once" where I move the kit when ... you guessed it ... I used it once. After I used something twice, I move it to the designer's file.
When I was on designer's CT, I had separate files for each designer, and always a special file for the kits I still needed to work with.