First, go read: The Rogue Scholar: Emergency Record Management 101.
Now, a few years ago, hubby and I considered starting a business of helping people create inventories for insurance purposes. The article gets a lot of things right though, and basically the author suggests using a flash drive for the most important items (we were using CD-Rs), and he tells you what those items should be.
In Victoria, we are always worrying about the Big One -- the earthquake that plunges a chunk of the city into the sea and brings devastation to the region. Other areas are worried about flooding, tornados, monsoons, whatever Ma Nature has to offer. But smaller than that are house fires, landslides, localized floods, or even something as random as a truck going off the road and into your living room. Crap happens all the time, and people who are prepared will have one less thing to worry about.
Excuse me now, while I go rotate our emergency supplies and update our inventory lists....