I agree with advice NOT to shoot until the last possible image. There's no technical reason I know of, but as sure as can be, if you aren't aware of where you are, you will find a critical moment happening in front of you while you are fumbling for a new card.
Second point: I carry empty cards in the little plastic holders they come in. In turn, I carry several empty cards in a zip lock in my camera bag, and when I remove a "full" card I drop it in with them all, without putting it back into the small plastic box holder. At the end of the day I download my cards -- twice -- to two different hard drives: one in the PC and anther external to the PC. Then and only then do I put the cards into my camera, format them and either leave them in the camera for the next shoot or put them back into the plastic box holders. Am I paranoid? Probably. But I have not lost an image in years. In fact, I keep another external hard drive at a neighbor's house a block away. I swap external drives monthly, update the one coming home, and then proceed. Why don't I use outside data back up services? They are businesses. Busnesses fail or disappear. Again -- paranoid? Probably. But I used to take pretty good care of negatives, and I still have them too!