Prepping for a survival situation is not an exact science. The reasons for someone to start prepping for an emergency situation range from natural disasters like hurricanes, tornadoes and floods to things like solar flares, volcanic eruption or even pandemic disease situations. So with that said there is not just an exact formula for how much of a food supply you should have in your emergency survival stockpile.
Before you try and come up with an amount first you need to choose what type of situation you are prepping for. If you are prepping for a situation where you might be without power for a number of days then a 72 hour survival kit would probably be fine. If you think that a solar flare may take out the power grid, or an EMP that did the same thing then you'd probably want to go with at least a 1 month food supply or longer.
After you are done reading this go into your kitchen and assess the amount of food you would have if there was no electricity. Your freezer and fridge will not count. You'll have what's in a pantry or cabinets. Now consider what items would need to be cooked to be useful. Although you could have something to cook on in a situation with no electricity, most people do not.
Now that you have done that, how long do you think that amount of food would last your family? Things like canned foods, packaged foods that could be ready to eat and other staples would be about all you would have left. For most people that's not much really.
Now that you have assessed what you would have left you need to think about what you will need. Would dehydrated or freeze dried food be ideal? Or would have extra rice or pasta and items such as that be what you need? There are also items such as survival food bars that can get you through many situations.
All of these thoughts weigh into what survival preparations you make before you are in a situation and it's too late. As a general rule of thumb I would recommend that you have at least a 30 day supply of food on hand. For most situations that's longer than the outage would be so you should be okay. If hyper inflation deprove gas prices up there might be a shortage of food but it would have worked out more than likely. A one month food supply can be bough for around $ 50 to $ 100 dollars. It's a small price to pay for having the security of knowing your family will be safe from most disasters.
You can also purchase 3 month, 6 month or 12 month survival rations which would have added insurance should something cause you and your family to go into survival mode.
Hopefully this will help you with your survival planning.