Depends on when you can plant it, when you want to hunt it, and what you're able to invest in it. The simplest is the rip-up-the-ground/stuff-some-seeds-in prepackaged bags of roundup-ready crops. Till, plant, spray, and you'll have food for the critters within weeks. In my opinion however, you can't go wrong with winter wheat as a cover crop for the perennial clover/alfalfa/legume mixes. These will last you for several years with only occasional mowing thereafter for maintenance. If you want a near-instant food plot that you'll need to replant each year, beets and brassicas can't be, well, beat. If you've got nothing but time, 2 acres of really good standing corn is a magnet into January.