I think ( shoot me down in flames if i'm wrong ) its from the Survivalist Mentality of not making the assumption that Just because Yesterday was like Today , Tommorow will be the same.
To Prepare ( 'prep' ) by putting essentials supplies of food , water or purification and other equipment aside and generally making some preps to ensure safety and well being if events occur.
Now , up to you how you view that stance an preparation , I guess your or mine perception of it may be altered if we have ever experienced or witnessed events that can seriously upset our normal life.
Power Cuts
Storms
Snow
Zombie Armada led by Lych king Napoleon In the Irish Channel.
To Prep , to make preparations.