Recent events in Japan have highlighted the need for emergency preparedness, whether at home, in the car, or at work / school. Do you live in an area where, given the occurrence of a natural (or man-made) disaster, you might face the possibility of being without food / water / electricity / natural gas / gov't services / etc, for anywhere from a few days to a few weeks? Having lived in California for almost my entire life, I've experienced a fair share of earthquakes, yet it wasn't until I was in my 30s that I seriously considered having any type of emergency preparedness kit readily available. While some may think such considerations to be examples of paranoia, I tend to agree with the motto: "Prepared. Not scared."
So, should you have an emergency kit and, if you do, what should it contain? First off, I'm no expert in this field, and I'm simply relating data I've gathered through research and experience. That said, my answer to the question of whether one should have an emergency kit is a resounding YES! However, while commonality of survival practices will dictate the main contents of the kits (e.g., food, water, first-aid), context will dictate many of the specific contents. For example, not living in a hurricane prone area, I am not too concerned about the effects of a Category 5 storm blowing through, and since we're not in tornado alley, I have no tornado bunker or strong-room to maintain. However, I have implemented earthquake related safety measures (e.g., bolted bookcases to the walls, have a gas / water shut-off wrench available, keep footwear near the bed).
There is a plethora of information available on how and what to stock in your emergency supply kits. To assist you, many of the sources I have used are listed at the end of this post.