Having good, reliable spares can be amazingly helpful.

When my oldest was about seven, she was very much afraid of the dark. I rousted her out of bed suddenly and rushed her to the downstairs bathroom due to a nearby tornado. Just as we got there the lights went out. That room is darker than ten feet up an elephant's you-know-what when the lights are out. She freaked.

Because I had a spare light to put in her hand, I was able to use another one to collect one of her wayward little sisters and the dog and get my family all into the room, without her screaming fit to wake the dead or clinging to my leg the whole time.