I don’t think we have a term for people who quietly keep a well stocked pantry, have a water setup, garden, have hobbies like canning, etc. That’s just being a bit rustic/prudent I guess. So then, the “prepper” derogatory label is only applied to the people who do it in the action movie/silly way. But, the question of how prevalent they are is a good one…
Mormons have a widespread cultural practice of prepping, which I understand is mostly the sensible kind where you keep stocks of food and water onhand in case of a natural disaster (rather than the generally-less-sensible rifle militia LARPing). This is something that the institutional Church of Latter-Day Saints encourages among its members, and it strikes me as a pretty good thing to do. Nonetheless, there's no reason why you need to accept the other religious tenets of the LDS church in order to do sensible emergency preparedness, and I'm not sure that not every Mormon community or household is equally diligent about preparedness.
Well, we did have a term for it until it got dragged and sensationalized in the media. I'd tell you that's a standard "psyop" that the propaganda arm of the government often uses against communities and subcultures that they want to discredit and suppress for one reason or another but then you'd probably call me a conspiracy theorist[1].
[1] another example of a successful smear campaign