When you flip the Full/Empty tab one way or the other and close the GUM case you can see at a glance if you have any room for more pictures.
I take lots of pictures that I use for the paper models that I design for ss42.com. When I am out taking pictures I need to swap out SD cards in my camera. But the SD card cases are different sizes and they take up too much space.
Step 1: The supplies
I found that the case for Sunstar GUM soft tooth picks http://www.sunstargum.com/index.php?id=3791 are the perfect size to hold 2 SD cards side by side. For me, I have bunches of the cases left over after I use up the picks. You can find these at any drug store for $3.xx or a 10 pack at the 99¢ store.