I've done the ISO thing and once left the camera turned on when I put it in the bag and came back to both batteries flat. Luckily I have two more, so I was still good. Have not forgotten to put the card back in the camera, although I almost did the other day, but I do have a spare two gig in the bag. I think I may get another eight or maybe a 16 gig card now 
I also put on my 50mm lens once and wondered why I was getting a lens error whenever I turned the camera on. Turns out I bumped the aperture ring when taking the lens out of the bag, glad I figured that out fairly quickly.
At least I learned from every instance, photography has been a great learning experience for me so far, and I know I will be learning more and more!
Chef Jay
I also put on my 50mm lens once and wondered why I was getting a lens error whenever I turned the camera on. Turns out I bumped the aperture ring when taking the lens out of the bag, glad I figured that out fairly quickly.
At least I learned from every instance, photography has been a great learning experience for me so far, and I know I will be learning more and more!
Chef Jay