I basically do the same as Barbara, though I also keep things separate by store as well. If you are on a CT for anyone, you need to keep the kits together and within the store(s) where it's sold for crediting. I try to stay with one kit at a time and only add items that I need to use from another kit (recoloring as needed), rather than just doing a mashup of disparate items. Generally, the kits will have a theme, so that's also important, or a "look" such as vintage, realistic, doodly, whimsical, etc. Not always a good idea to mix up the various looks, themes, and color schemes...
One thing that really helps is getting things orderly when you unzip and put away. Some designers fail to name their elements, so I go through and put the generic names on those (flower, ribbon, frame, etc.) wherever they're missing, making it easier to find a particular needed item when doing a layout. In Bridge you can search for "frame" for example, within a store or designer's kits to find all the frames with "frame" in their file name. You can also tag items with color and look or theme if you desire to go that direction. I find that too daunting, and just use the name for searching. Once you get a lot of kits in your stash, you definitely want to be able to find what you want.
Another thing that helps me is to make sure there is a preview in the root folder so that I can see the general look of the kit without delving into the papers folder, elements folder, etc. You can even give the folder icon the preview image itself so you see it in the Finder (Macintosh) or Explorer/whatever (PC).