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.