I drove from Portland down to Bend, OR yesterday to camp with some friends up in the Cascades. I didn't want to take my full kit, so I just put my 30d and two small lenses into a Sling 100. Once I had my tent all set I pulled out the camera to do a little shooting. Fired off my first click, check the screen only to see "No CF Card" Grabbed my P&S, same deal.
Turns out I had taken both cards and my card reader in my computer bag to the library to do some PP and email some pics. As soon as I got home, I remembered to put the reader with the cards back in my big bag, but didn't put them in the cameras. When I swapped bags I forgot to take the cards along. Lesson learned, but I missed some great shots.