Here are some links to data on the U.S. food system:

http://www.energyfarms.net/node/1389

Looks to me like the total food system consumes about 10% of U.S. energy use, with on farm consumption (including embedded energy in fertilizer, pesticides, tractor fuel, etc.) about 1/4 to 1/5 of that 10%.

The most energy intensive part of the U.S. food system is actually home storage and preparation.

I have been learning a lot about grain production lately as working to sow wheat. Conventional grain yields are incredible (about 6000 lbs/acre of wheat in CA) and I don't expect to approach those with our organic, low energy, dryland methods. And, we need to rotate fields with cover crops to put nitrogen back in. So, I expect yields half to a quarter of conventional when sown, and to only grow wheat half the time. In total then, I expect to get a quarter to an eighth of the yield for a given area over the long term.

But, I do expect to have a very positive net energy!

As a food engineer, let me tell you this is the case. something like 4.3 trillion dollars of food are turned over in the USA per year. Food goes into plant one place, comes out as prepared meals, canned goods, meats at another. Obviously different plants for different products, but usually we are constrained by a large problem:

Keep the water content as high as possible. (sell the rubes as little real food as possible)

Keep the weight down. As water is the #1 component of foods, this is in direct conflict with the above point. Less weight means less volume and cheaper transport!

You would be both surprised and disgusted by the amount of water shipped in packaged foods across the country.