Batteries. Always carry some extra batteries.
Or remember to check battery level and card space, ahead of time?
At least twice I've had decent bucks wander up fairly close while I was hunting turkeys and discovered my pocket digital's batteries were at the end of their rope.
Another time I had a good whack at a critter pic and the card was full. By the time I deleted a few images, the moment had passed.
Sucks to be old and forgetful.
