A "prepper" is someone who prepares for a S.H.T.F. event (this is actually their terminology, not mine).
This S.H.T.F. event can be anything from an earthquake, a flood, crash of the economy, war, etc.
The idea is to last long enough for help to arrive.
Most preppers will have some water and food (and toilet paper), and some even have a secret hiding place away from the populated areas, etc.
That's not a bad idea reagardless of what the situation is.
For an idea of what prepping is all about, please click here.