I understand it as, "That's not going to win you a goodbye lunch." The 'goodbye lunch' is the farewell for an employee, tucked conveniently into lunch hour. To say, "that's not going to win you a goodbye lunch" means that your reasons for leaving the job (or the way you go about resigning) won't be appreciated by the bosses, so it's likely they wouldn't buy you lunch as a thankyou - you'll simply leave without ceremony.