Ramblings of the Mad Farmer:
Bah. Reduce the amount of stuff that grows in the wild, but make it grow back (a la Elder Scrolls). Those plants you find out there survived reason...perfect soil, etc.
Keep farming in general, but make it subject to all kinds of lousy things...seedlings die as often as they thrive. Plants produce random yield from 0-2 (mitigated by perks, but 0 still always a possibility). Make crops subject to trampling like in earlier 7D2D versions. Plants also just randomly die. Realistic farming that helps the "too much food" problem, but with perks and a lot of effort becomes a meager means to live off of.
If nothing else, bring back trampling!....nothing more ominous than the sound of a pack of zombies you can't see directly cutting their way through a cornfield. You're like "I ain't goin' in there!...but...the corn!!"
-Morloc