December 18, 2010 No Comments Free 16 oz. Shake at Whataburger on Sunday Print out the coupon and redeem for a free 16 oz. Shake at Whataburger on Sunday. Offer valid only December 19, 2010. Location. Free 16 oz. Shake at Whataburger on Sunday – EXPIRED Facebook Twitter Add Comment Notify me of follow-up comments by email. Notify me of new posts by email.