As much as I detest organised religion, the Mormons have a pretty good take on this. They strive to have a six month supply of food/water/cash on hand at all times.
If you've only got two days supply, you may not be so generous.
[1] My elementary schools had a good program of bring in canned food at the start of the school year in case of emergency, have a picnic to eat it in the last month of school. I also did have a disaster can when I lived in California; I'm less prepared at the moment.