Unless you are a part of the top 1% in our economy, your financial situation doesn't allow you to purchase mass amounts of food and supplies to stockpile. However, bartering with others after a disaster might be a solution to any shortfalls in supplies.Bartering is a method of trade that will rise after a disaster, especially if currency is worthless. Many people will use bartering as a means for survival as supplies get low.
By choosing a specialty item or service, you can make yourself more valuable to society as rebuilding takes place. Using these goods or services allows you to trade for valuable items to increase your survival rate. Some examples of goods I will barter include medical supplies, clean water, ammo, garden vegetables, and honey. I even wrote an article about liquor being a prime bartering item. Medical doctors, gunsmiths, leatherwork are an example of services that are easily traded for supplies.
Those that have not prepared will dwindle in numbers from disease, hunger, violence, and thirst the first couple of months after a disaster. Even the people that have prepared will see hardships, though less common. When the population begins to decline, it is perceived that the threats will too. Because humans are pack animals, survivors will begin communicating and forming villages in order to improve survival. Your role in society will be determined by the skills and goods you bring, so make sure you are valuable.
As you stockpile, choose some items to stockpile more of for bartering opportunities. Also learn about hobbies like beekeeping or gardening so that you can provide renewable goods as well. Renewable goods will be invaluable to your survival because you will hopefully never run out.