Using a Brother P-touch labeler, each card is labeled on one side alphabetically with the capacity of the card.
Cards are normally stored in a Think Tank Pixel Pocket Rocket. We also use the Gepe Card Safe Extreme when shooting near water or in a location with lots of sand/wind/dust.
All the cards are checked and formatted in-camera before every shoot and are stored in the memory card holder with the P-touch label facing out. This lets us know at a glance that these cards are blank and what the capacity of each card is.