To get an idea on what a prepper is take a look at this: https://en.wikipedia.org/wiki/Survivalism .
I was raised in a big-ish city (Constanta) in a country (Romania) where we have 4 distinct seasons and one of them in particular (winter) is quite harsh so common sense there is to keep some food in your cupboards or freezer just in case your local store runs out of stuff (when winter hits there’s transport disruption which then leads to delayed or missed deliveries to local stores which means you will not always find the products you need / want when you need / want them)
With this in mind and, considering I have a wife and children who I’m providing for, I need to make sure we have the lifestyle we want moving forward which means even when shit hits the fan we need to have fresh water, food (all major groups), medicine (your basic pain killers, disinfectant, bandages, etc), spare clothes, hygiene (soap, tooth paste, etc), access to information (books, magazines, newspapers), electricity (powering various systems for telecommunications – radio/tv) for a long enough period of time (depending on what you want to prepare for).
If you ask me, your average family should have enough stuff stored to last something like a few weeks (up to a month) because under normal circumstances you average store – even when weather is bad – will get supplies weekly or biweekly , your power plant is always on but the power lines, even when down, should be fixed within a few days up to a week, your telecom line if broken will be fixed within a few days, and so on. This makes sense under normal circumstances and is a good practice (even the government recommends storing stuff for a few days) so i strongly recommend everyone to do it regardless of where you live on this planet.
This will cover most cases in a civilized society and might be more than enough for the average family but then there’s always that “what if?” question that might get you thinking. What if a huge storm or an earthquake hits and disrupts power lines for a long period of time (say 2 months) ? – your fridge will stop running so food will spoil, your tv/radio/phone will be offline, your PS4/Xbox will no longer be there to help you relax, your security system (if you have one) will be useless, etc. What if a nuclear power plant has a problem with one of its reactors (like Cernobil or Fukushima) and there is a radiation cloud coming your way? What if war starts in your region ?
What if … ?
Me and my wife thought about it and know what we want to do next (will share some of our projects in time) … hope you have too.