Its a reason to convince yourself to buy things you want but can't otherwise justify as useful, that will be used in an emergency. I just stock my truck with MRE's etc cause its always with me and have dipped into it a few times for matches etc. Other people would use it to escape civilization that is collapsing. I'm staying home if anything bad happens cause small towns are awesome. Its always good to plan for emergencies and putting supplies together for problems is smart if you can afford it. I have mres, a water filter, crank radio(walmart),rope, and a tent in mine. Plus like 8 knives because I buy every one I see and all the drawers in the house are full.

I have 2000 rounds of .22 long rifle, 100 in .204 ruger, and 200 in .284 win, around 300 12 gauge shells of different shot and slugs, 5 gallons of water, A few dozen MRE's and mountain house's, a jet boil, big box of matches, tent, blankets, a katadyn pump water purifier, basic fishing gear, rope and other outdoor basics in my "bugout" set up. it wont fit in a bag but it fits into my truck and will keep me and my family alive for a few days. it is more about being prepared then waiting for all hell to break lose.

I have mini bags for the vehicles, that I update via the season, you need shelter(poncho,space blankets,gloves) water,fire, and tools.
for my car my bag has the above and duck-tape,vise-grips,multitool,electrical tape,gloves,zip ties. I picked up some S.S. zip ties which are great for emergency repairs.