sitting here the other day, and i looked at these post-it tags that i usually use to mark pages in books, magazines, catalogs, etc..at work, and thought they would work well to mark empty cards and full batteries (especially since they're green).
a very simple idea, but it has worked very well for me to be able to manage this, and not guessing if i have dropped a dead battery back into my bag after a shoot.
when i use the card or battery, i simply throw away the tab, and replace it when i get home and charge or dump the card on the HD.
the tab is also most helpful at removing the CF cards from the gepe card case, it's a VERY tight fit, and before using these, was a struggle to remove them in a hurry.
thanks to the folks over at petapixel for featuring some of my ideas on their blog. it's a great site for info and ideas on everything photography. if you haven't checked them out, you are definately missing out!