I doubt anybody needs to prep, but if a person has enough money and it makes them feel secure, it is okay.
I got some of my ideas from living in Africa and thinking about the food aid that was given to the poor villagers in need. I couldn't remember the exact proportions of food being handed out as emergency food aid in Africa so I found this qoute "Each family has received 50 kg of rice, 25 kg of beans and 10 litres of oil. This will help farmers bridge the gap until January, when they will be able to harvest from seed the ICRC has also distributed." The basic point was that when a person was starving in Africa, they dropped off a bag of rice and beans, and a bottle of oil. The qoute dosn't mention it but they also got a small bag of sugar.
I then calculated that calories per kilo.
1 kilo of beans = 1300
1 kilo of rice = 1280
1 kilogram of coconut oil = 8600
I reduced the amount of oil from 10 to 6 kilos because that was a lot of oil.
64,000 calories from rice (50 kilos)
32,000 calories from beans (25 kilos)
51,000 calories from oil (6 kilos)
147,000 calories = 3 months (1630 calories per day)
To buy the food would cost around this much giver or take.
3 5-gallon buckets of rice $60
2 5-gallon buckets of beans $100
4 1.5 kilo buckets of coconut oil $100
The buckets $50
The mylar bags for holding food and oxygen absorbers $20
Total estimated cost: $330 per person, per 3 months.
The basic thing when trying to make a meal is that there is the right balance of carbs, protein, and fats. As long as somebody has those things that can eat the same thing day after day after day. Lots of people around the world subsist of of a single staple food that makes up the majority of their meals. Here a person has three!
It is of course really important to have a bunch of seeds in another bucket and also to have a book or printed up guide of how to forage for wild veggies. As the qoute I mentioned above also points out.
If a person wanted to really go all out, then add some more kinds of beans and/or lentils and add a bag of sugar, a huge tub of honey (doesn't go bad), powdered milk, salt and bullion. Gallon of distilled white vinegar, and huge tub of baking soda. Adding these things should still keep the price under $400 per person but really aren't necessary.
If stored correctly, such as in a cool dry place with no light, it should last a lifetime. The exception being the coconut oil for which one might want to replace every 10-15 years.
The last thing is that assuming that somebody is in such a dire situation that one needs to eat this emergency food, we can assume that there also won't be any water, gas, or electricity being serviced to a person's house. Obviously, first and foremost before prepping food is making sure that there is a good source of water. This might mean finding a natural source of water like a sring or lake near by and having a means to purify the water, but also it is important to have a way to cook the food. At a minimum I would suggest a fuel effiecent camping style stove that burns wood $100-$200 but they problem with these types of stoves is that they literally send up a stream of smoke that drifts through the air and can attract unwanted attention from far away. A far better option is a solar oven. With a solar oven, a person doesn't have to collect firewood and there is no smoke and no smell. A solar oven also gets more than hot enough to cook rice and beans just using the suns natural energy. It even works on days that are a little cloudy for warming food. On a hot day with good sun, it can definitely boil the water that will later become drinking water. That will be another $300.
For the water filter, which is arguebly the most important thing on this list, I had something very simple like this in Africa.
http://www.regenerativenutrition.com/water-filter---stand-alone-p-112.asp This set-up was more than good enough to make dirty pond water drinkable. The process is easy, first boil the water for more than 5 minutes to sterilize the water, and then pour into this system and let gravity filter the water sparkling clean and potable. Many people will advocate complicated systems, but a very simple system like this with extra filters can be bought for under $150 and will clean enough water for a family of 4 for a year (I would say at that point might as well get some extra filters for some additionaly years too).
To get the ovens and water filter will add another $250 - $600 to the budget, which is a one time start up cost of course, but a minimum get the water filter. It is actually more important than the food in many ways.
As I said, water is the most
And lastly, and I am kind of sad to say it, but if a person is going to go to all this trouble of buying this food and prepping it, one might as well get a shotgun and a whole bunch of shells too because there is a very good chance that a person will have to defend there food or be prepared to give it all away when people come looking for food which will be inevitable. Another nice thing to have would be one of those wind-up/solar radios that can listen to broadcasts from far away.