u can't stock food for much of a time span, but you can stockpile non hybrid seeds and cultivate them in well hidden, small plots. For the time period right after most people are dead (ie, 6 months after shtf) it might be best to stick to growing just sprouts. then your crop is ready in a few days, not months, and you can easily abandon 1-2 little plots and start again elsewhere, if enemy presense seems likely or is obvious.