Three reasons I prepare. My church encourages all to have a 3 month supply of food and provisions, link below for great resource. Going through Hurricane Andrew (we were on the outskirts) was pretty good inspiration. Seeing grocery store shelves literally empty, and people completely reliant on others to bring them food and water. I believe in the not too distant future our economy will crash. A great site I have found to help with how to do your three month supply is, food storage made easy. This breaks it down into "baby steps" for those of us who are a bit overwhelmed.
http://www.providentliving.org/channel/1,11677,1706-1,00.html
http://foodstoragemadeeasy.net/
