Here's a shocker: In the wild, lawless world of post-apocalyptic Earth, it sure will help if you have the ability to produce your own food.
Yeah, you'll scrape by on canned goods and military rations for a while. Fall in with the mutant hordes and cannibalism will provide necessary protein, as well as some unnecessary prion disease. But eventually even the Twinkies will go bad, and the meat of your fellow man will become harder to come by.
So, you'll need to grow your own vegetables. If you can't live without meat or fancy your hunting skills, you'll need to know how to preserve your food. Have you ever pickled a beet or a pig's foot? Know how to make beef jerky or fruit leather? Don't even get me started on beer and wine.
Without the aid of large-scale industrial agricultural techniques (or chemicals), you'll have to turn to the traditional farming methods. In rural areas, this might mean family gardens. Amid the ruins of major population centers, you'll want to seek out the guidance of the hipster pickle enthusiasts, beer brewers and urban farmers. With any luck, they'll take you under their wing.
Also, they might practice a little cannibalism on the side, so keep your guard up.