I think there are many reasons for at least a temporary SHTF if not TEOTWAWKI scenario to arise. Natural disasters are a big one, from common recurring events like massive Cat-5 hurricanes (I am a Katrina survivor), earthquakes and resulting Tsunamis, to rare yet inevitable ones like killer meteor strikes, Super Volcanoes (like Yellowstone) eruptions. Then there are the man made disasters, like accidents and terrorist acts involving nuclear (including EMP), biological and computer virus weapons, to civil insurrections resulting from political movements, trade wars, hyperinflation and the resulting economic crashes and even old school invasions. I think the most likely SHTF scenario will be localized in nature, such as from natural disasters, so being mobile gives us a distinct advantage to those with a bunker mentality. Small, highly mobile, sustainable communities with diverse skill sets (such as prepared, independent, but like minded rubber tramps) can move, assemble in an area in short notice, and when threatened, can disassociate and dissolve back into the faceless crowd, making us impervious to a group attack, ensuring most survive. The key to the success of this strategy this would be reliable, secure communications. Any suggestions on the best way to accomplish this, post internet/cell towers?
The definition of a Zombie, to most preppers is the unprepared roving horde, the occasional skilled lone raider, or roving bands of post apocalyptic brigands (think MS-13 meets Mad Max) who come along either after a homesteaders crops are ripe, or after their crops have been harvested, with the intent of killing them and stealing what they have (even if it's just to eat their fresh corpses.) This is why the mobile survival scenario makes more sense, as you are not a target of opportunity to every Tom, Dick and Zombie that comes along. It makes sense to have some provisions, weapons, etc. but more sense to adapt to your environment, using it as camouflage to keep from becoming an easy target.
Anyone who's seen the series Firefly or the movie Serenity knows what a reaver is. If you look like another reaver, the real reavers won't target you because they think you have nothing they want. BTW there's a large decal on the back or my motorhome with her name, Serenity.
Burn the land and boil the sea, you can't take the road from me, since I've found Serenity.
Chip