According to the National Oceanic & Atmospheric Administration (NOAA):"The current average lead-time for tornado warnings is 13 minutes."http://www.noaa.gov/features/protecting/tornados101.html
What can you do within that 13 minutes timeframe?
Certainly argues for having a shelter pre-stocked (whether a below-ground shelter or interior bathroom) with flashlight, first-aid, battery-powered radio, etc.
I've also noted in the images out of Oklahoma that even the worst-hit vehicles at least seem to be intact, as opposed to the residential homes which were obliterated. Argues for having sturdy leather work gloves and first aid, blanket/towels in cars to use in the aftermath of your own home's damage or to help rescue others in the debris.
If you were now living in tornado alley, what would you put in your child's school bag (backpack) that might be helpful if they were trapped in the rubble of a school?
Seems to me that a whistle, bandanna, bandaids, little flashlight would be good things for them to have at all times and especially in a crisis. Of course, they may not be near their bag when something happens but they might be.
I'll be adding OKC to my litany in response to the question: why prepare?
As little time as 13 minutes seems, there is zero notice for an earthquake or terrorist attacks.