Upload & Sell: On
I keep them in their original plastic cases. I store multiple cards, in their individaul cases, in the small pockets of my usual bags. Sometimes, I put them in a small Otter Box, if I'm going to be on the water, in something smaller than a 'ship'.
I use sticky tape, file tab thingies to let me know which cards are full, and which are not yet used. A tab across the latch of the card case door means it's not used. A tab across the side of the case means the card is full.
I also use coloured electrical tape to show me the capacity of the card that's in the case; yellow is 64GB, red is 32GB, smaller are clear (no tape).
I'va attached an example photo that shows, in the foreground, an empty 32GB card on the left and a full 32GB card on the right. The two, empty 64GB cards in the background are in an Otter case (model 1000), which is an excellent fit for six CF cards, in their original cases. Also bulletproof.
I use the same system for SD cards. It's just that they're too small to find, at the moment.