We also aim for $100/wk ($5200 a year) for our food, with varying levels of success.
It is totally doable if we don't go out to eat, which with our new daughter has been less of an issue. :P
We plan our week of meals and do a trip to Trader Joe's or Aldi's, it is pretty easy to get out of either of those with a week's worth of food for less than $100. We also live close to a Whole Foods, but that is a different story.
This week, we had left over chicken noodle soup from the week before, then we had slow cooker pulled pork, and leftovers another night over rice. A huge pasta casserole, which was good for another set of left overs and a lunch for me. We are making a slow cooker chicken stew tonight, which will give us dinner tonight and tomorrow, and then we still have some ground turkey that will become a turkey lasagne for over the weekend. I also buy baking supplies (flour, bread flour etc...) for occasional homemade bread.