This is a pretty good article on 72 hour kits.  The author's site has some very good information on it as well.

--Jason

72 Hour Emergency Kit

Emergency preparedness doesn't have to be expensive and you don't have to buy special survival gear and supplies. It's quite easy to assemble a basic 72 hour Emergency/Survival Kit with a trip to the supermarket and hardware store. That doesn't mean it will be the lightest possible kit, nor take up the least volume, as if you used specialty products, but it will suffice to keep you going when things take a turn for the worse.

Elsewhere on Equipped To Survive™ you'll find a fairly extensive list of gear and supplies to possibly include in what some might call an "Ultimate" Disaster Preparedness Kit for your home and family. In this article we'll look at a very basic kit that would see you through most emergencies. By basic, we mean just the essentials and little more. Prudence suggests you'll probably want more and every kit needs to be adjusted to fit your own environment. If you live where is gets cold, you may want to add more stuff to keep you warm, for example. This is true no matter if you assemble your own kit or buy one of the many commercially prepared kits.

The industry over the years settled on 72 hours as a reasonable length of time for which you ought to be prepared. This is based on historical evidence that suggests that by the end of 72 hours, at least in first world countries, government services will normally be restored to the point that you can avail yourselves of them without major difficulty. What you are trying to prepare for is to be able to take care of yourself and your loved ones during the first hours and days when government and volunteer services may not be able to respond as fully or quickly as anyone would like. The reality is that it takes time to organize and marshall the equipment and people needed, you may well be on your own until then.

The complete article can be found here:  http://www.equipped.com/72hourkit.htm