You should go to Whole Foods on Sunday and pick up a rotisserie chicken for $5.99. (I went for the herbed crust, but there are other flavors.)
Then, go to the deli section and pick up a container of potato salad (retails at $8.99). But you're going to get those potatoes for free because then you find the WF periodical on one of the many racks around the store and tear out a coupon for the free side you get when you purchase a chicken.
To complete your meal, pick up a container of organic greens and salad dressing. I've personally had the ranch and balsamic vinaigrette flavors, and both are great. I think these will run you about $5.99 (I buy the big thing of greens) and $3.29, respectively.
Take it all home and enjoy immediately. Continue to pick on your chicken, potatoes and salad as long as it lasts you in the week! Best meal (with leftovers) for less than $20.