So far I've got about 6 micro SD cards of various sizes, and I'm soon buying a couple more 32GB cards. They're kinda tiny so I've always stored them in the SD card adapter that comes with them to make them easier to handle, however I needed something to store those in so they don't get lost. So recently I found this Micro SD Card holder on Amazon that's credit card sized. A standard credit card is .040" thick. This holder is .100 thick, a little over twice the thickness of a standard credit card. I really don't plan to put this in my wallet, but I could. I received the holder today, it's the bees knees. The slot tension on the SD card is just the right to keep them in the holder without accidentally sliding out. Some of the Amazon reviews said the tension was too much, but it's just right IMO. It provides an area to write on for each slot, to name each card, if you feel the need, such as 16GB, 32GB, 64GB, or USED, Empty, etc. This is a very handy holder, $10. How do you keep track of your SD cards?