Here is a sweet tip we got from Adam Frimer about managing your cards while on a shoot. You start with a bunch of clean formatted cards. Place them all in a hard case facing up. This way you can see the data on each card. (Those hard cases are about $10 on amazon)
After using the card and filling it up, return the card to the case with the text facing downwards. This will indicate that the card has been used and it is not empty.
This is a quick way to know which cards can be used on the next round of loading and which should be downloaded to a computer.
This is not a new trick, Adam tells me he picked it up from Rich Harrington, and we have been doing the same with batteries forever. If you own a soft case (my fav is the TTP Pixel Pocket Rocket), This will work too. Just insert the cards into the pockets facing forward or backwards.