After you have slayed, mutilated, fried and crushed hordes of zeds, you should start to consider doing other things not so cool, but as important for survival. Growing your own food. If you live south enough (say, Mediterranean/Florida), you can start just planting the seeds to your back yard, but if you live any norther you should consider building a greenhouse. It´s not that hard really, all you need are a hammer, nails, some 2x4 and lots of plastic wrap. (You could use glass, but it takes much more time and you need more tools.) Build the frame of your greenhouse out of the planks and wrap the whole thing to the plastic wrap. This "building" of ours is not very durable to bad weather, so you should start searching for glass or a ready abandoned greenhouse, which you can take the glass out of, for you to use. Until then, prefer taking the greenhouse indoors when the weather changes to windy or rainy (garage/basement, if it is too big for either one try using a big plank or such to cover it, the plastic wrap is the weakest link). During rain, it also takes care of irrigation.
Place the greenhouse to a safe area. If your backyard is fenced I would place it there. If the winter is starting to come, you can no longer use the plain ground, because its temperature is no longer high enough for those vegetables. You should build a foundation for the greenhouse with concrete, and make a layer out of an insulating material between your growing food and the ground. This keeps your food safe from the cold, so now you only have to take care of getting water for them. If your backyard is not fenced or the fence doesn´t keep the zeds and raiders away for a minute so you had time to escape from your greenhouse, you have two options: fence the backyard (risky) or build the greenhouse to your roof (less risky, but a lot of work). If you build your greenhouse to your roof, it has some (un)desired effects: raiders can see from a long distance that your house is inhabited, although it is also a signal for other survivors. Your greenhouse is more affected by the wind conditions. Your vegetables get more light, because there are no trees or other obstacles to cast a shadow upon the greenhouse.
To get tools and other equipment to build your greenhouse, including seeds, mould and fertilizers, I would consider raiding a hardware store. Hardware stores often have a gardening section, where one can get tools, plants, seeds etc. (this is the case in Finland [my home country], I´m not sure about the situation elsewhere.) If your hardware store doesn´t offer this kind of service, you should improvise. Flower shops may have fertilizers and mould, seeds can be acquired from a farm or other greenhouses. (Extra Info:http://en.wikipedia.org/wiki/Agriculture)

About Irrigation:
Your plants need water. If you know the rough amount of water the plants need, stick to that. (the plants aren´t too picky) However, if you don´t know that, but you know that the plants are grown in your area, the safest bet is to construct a pool that has the same area size as your greenhouse and use the rained water gathered to that pool. If your area is too dry/wet for the plant, change the pool size accordingly. Search for literature about the subject, knowledge is power. Do not use your drinking water for the plants. If your plants dry out, you have 2 weeks to 2 months of time to search for food before you starve. If you run out of water you have only 2 to 4 days to get water. Always look for another source of water, I think using rain is the smartest move.

About Animals:
Do not use the food you have grown in your greenhouse for animals. If you eat the vegetables yourself you get five to ten times as much nutrition compared to giving it to a cow and fattening it for you to slaughter. Try to feed your cattle and such with food you can´t use yourself. (grass, hay) The best efficiency rate is with chicken (2 kilograms of food->1 kilogram of chicken), and they lay eggs. Omelet for breakfast isn´t the worst food you could get in a post-apocalyptic world. You can use animal feces for fertilization. In very long-term planning, don´t keep animals after they have reached their full growth, unless you need them for reproduction; at that point it is the wisest move to slaughter the animal, take the meat and dip the meat to salt, or if you have electricity to refrigerator, so you can use it later.