Green’s Dictionary of Slang

prepper n.

1. (Aus./US) one who prepares for an extreme situation.

[Aus]G. Disher Consolation 83: Leon had turned weird a while back and gone all doomsday prepper.
[US]T. Pluck Boy from County Hell 317: His compound was on a big piece of land with a barred gate and a berm built around it as a defense against both water and attack. A prepper’s paradise.
[Aus]A. Nette Orphan Road 65: ‘I’m not a Nazi, Carl, or some crazy doomsday prepper. I’m a racial realist’.

2. a preparatory school + sfx -er sfx2 (1)

[UK]J. Meades Empty Wigs (t/s) 134: Most of my muckers at preppers had dadas who were just as queer as Dada, even queerer.