I would add, plant things that look like weeds. Amaranth, quinoa (looks like lambs quarters), wonderberry (looks like deadly nightshade, but the flowers are white-to-cream instead of purple). There are also many plants that will look like their wild cousins simply by not being planted in rows (carrots, parsnips, sorrel).
Also, nurture wildlife in your area, and learn to trap. Traps are quiet, gunshots make noise.
Very good points. Things we take for granted now are going to look and sound very conspicuous if it all grinds to a halt.
Some FReeper made a comment some time back that most people wouldn’t recognize a potato plant if they tripped over it. He suggested planting them at random in wild areas.