This is a survival-food pyramid. This is a good indication of how things could go, and what level you should be prepared for.
As you can see, the Immediate is to be prepared for a power outage or storms is what you'd have your bug out bag for. A three day supply of food and water and a camp stove and fuel.
Next is the Extended, being prepared for up to three weeks without power or utilities. Civil unrest, tornado or major storm could be the causes. You'll need some bulk supplies to see you through this one . Large containers of water, groceries and kitchen supplies.
When you get to the Long Term, this where the rubber hits the pavement. You are now looking at up to three months or longer. This can be the result of a earthquake, a hurricane, longer civil unrest or from major crop failures. You now need some serious supplies. Your water will probably run out, so you'll have to have a way of not only collecting it, but purifying the water. Depending on your survival food supplies, you may have to go out and do some fishing and hunting to get through this.
Perpetual. Now we're talking serious business here. This is where your survival food planning is either going to make it or not. Now is the time where you'll find out if you planned far enough ahead. This could be the result of a war, total collapse of the government or one major disaster after another. Now you have to look way ahead and locate a good water supply, start planting seeds for your vegetables supply, fish, hunt or trap meat, (if you have access), raise some kind of stock, and building more permanent type shelter. There is no grid, there is no stores, there is no gas station, your making do with what have and planned for.
Hopefully, you planned well!