If you head over to Think Tank Photography bags, you'll find that "Be ready before the moment" is their slogan. It's something that is critical in photography. You need to have your camera ready, your settings checked, the camera turned on, and the lens cap off to grab the best photos.
March 31, I grabbed my camera bag at the last moment before heading out to volunteer at a golf tournament. I didn't really want to sit at a table and sell 50-50 tickets, but I was prepared to do that if I had to. I was almost prepared to take photos all day.
I hadn't thought through what I'd be doing all day. If I had, I'd have cleared and freshly formatted all of my memory cards. I'd have charged up my re-chargeable batteries and I'd have made sure that I had spare sets of Alkaline batteries for both the camera and the flash. I made it through the day, but I didn't take as many photos as a real pro would have done. I was saving battery life when possible.
I've just spent a few minutes making sure that my gear is prepped. If I get asked to do something like that tomorrow, I'm ready. It isn't enough to own gear. Your gear has to be ready to use.
The March 31 shoot taught me that I need to carry at least 12 AA batteries to have a complete backup set. The camera body takes 8 and the flash takes 4.