Before you start on a program of home preparedness there are several questions that you need to ask yourself:
(1) What am I preparing for?
This list could include short-term power outage, seasonal weather like tornadoes or hurricanes, earthquake, unemployment, interruption to the economic system, collapse of the economic system, break-down of the social order, insurrections or riots, nuclear or biological war, electro-magnetic pulse attack, asteroid collision, and who knows what.
(2) Am I currently living in a survivable and defensible location?
Are you in a big city? (not good) Do you live in a small town? (better) Do you live in a rural community? (better still) Do you live on a farm at least two hours from a major metropolitan area? (very good) Are you well established on your farm with a good support group of like-minded neighbors? (best)
(3) What kind of financial resources do I have to devote to preparedness?
Preparedness is an investment, just like a bank account or stocks and bonds. Some people live paycheck to paycheck and don't have funds for investment. Don't let this stop you from preparing to the extent that you can. Some people have money to invest, but they spend it on things that they want in the here and now. Not a good approach to home preparedness or to life in general. If this is you, you're probably not reading this anyway. Some people invest in bank accounts, stocks, bonds, 401K's, life insurance, health insurance, long-term disability insurance, etc. A person with this kind of money to invest can easily redirect part of their investment to home preparedness. The amount would depend entirely on what level of commitment the individual wants to make, but I wouldn't cash in my 401K or cancel my life insurance for the sake of preparedness. Keep things in perspective. You're a lot more likely to retire than you are to get hit by an asteroid. I hope.
So how should you go about preparing?
I believe that no amount of food, water, medical supplies, tools, farming equipment, or coin can save you if someone else can take them away from you. Of course you can just chalk it up to me being a Texan, but the first thing I would recommend is a weapon to protect yourself, your family, and what you already have. If you will have only one weapon, I recommend a good reliable 12 ga. pump shotgun and a variety of ammo including bird shot, duck and turkey shot, buckshot, and slugs. If you want to invest more extensively in home defense and hunting weapons, see my posts on "Five Guns for the Homestead."
Depending on where you live, and what time of year it is; you could be dead long before you have a chance to die of thirst or starvation. Hypothermia, or the loss of body heat, can kill you just as dead as a bullet from an AK-47. You need a source of heat if the power goes out. It can be as cheap as a propane camping heater for the short term, or it can be as expensive as a high quality wood burning stove that will last for decades. There are many choices between these extremes so pick one that fits your budget and invest in some heat.
A source of light is not really necessary for survival, but it sure does make it easier. My power never seems to go out during the daytime. Getting to the breaker box in a dark closet to flip switches, and going out into the dark night to get the generator running is nearly impossible without some kind of light. If you're going to use flashlights, make sure that you have fresh batteries. Mine never did so I bought plug-in rechargeable flashlights that stay plugged into a wall socket until needed. I also bought several hand cranked flashlights. Again, light is not absolutely necessary for survival; but it's cheap and very helpful. Get some flashlights. I also have kerosene lanterns in every room, a propane camp light, and lots of candles for longer term situations.
Three days is about all that you can survive without drinkable water, and you need a minimum of a quart a day just to stay alive. A gallon a day per person is more realistic. Water is cheap. There's no reason not to lay in a supply of drinking water in plastic bottles. Several cases will fit under your bed. For longer term situations you can look into a cistern or a water well. These are both still very common in rural areas.
Food is where a lot of people start a preparedness program, but as you can see it's way down on my list. The explanation for this is simple. The average person can live for three weeks without food. Of course nobody, including me, wants to go that long without a meal. How much food to store and what kind of food to store depends on how many people you are feeding and for how long. I would say that the bare minimum should be one week's food for each person in your family. This would be for a short-term situation and could be made up of canned goods and dried foods. The longer that you are planning for, the more thought you will have to put into your food storage program. One thing I would definitely advise is not to store a bunch of stuff that you don't normally eat. Keep a rotating stock of items that you already eat and replace them with more as you consume them. I had a neighbor that bought buckets and buckets of nitrogen packed hard red wheat. He never ate a tablespoon full of it, and ended up giving it all away just before it expired. Lots of money down the drain.
Most homes have a medicine cabinet with basic first aid supplies and over-the-counter medications. That's a good thing, but make sure that they are fresh, and if you are running low on anything go ahead and buy a backup. The rule in my house is, "If you've used half of it, buy a new one." If you take prescription medications, you should have an extra month's supply of these on hand at all times. Also, do yourself a favor and buy a good home medical book and a Red Cross first-aid handbook. There are quiet a few posts on this blog about home medical supplies and it would be worth your time to read them.
A good battery powered or hand-cranked radio will keep you informed about weather conditions and other events that may affect your survival. You can get little battery powered radios for under $20.00. A good hand cranked radio with AM/FM, short wave, and weather bands can be purchased for under $100.00. This is money well spent. The radio that I have can also be used to recharge a cell-phone.
All of these things listed above are the bare minimum preparedness supplies that I would keep on hand. If you are looking to prepare for longer term situations please scroll through the posts on this blog. There is a wealth of information based on personal experience about how to prepare for almost any survival situation.