It's the last day to book a flight on Southwest Airlines without being hit with a fee to check bags after the airline abandoned a decades-long luggage policy that executives had described last fall as key to differentiating the budget carrier from its rivals. The airline announced the change in March, saying at the time that the the new policy would start with flights booked on Wednesday. Under its new policy, people who haven’t either reached the upper tiers of its Rapid Rewards loyalty program, bought a business class ticket or hold the airline’s credit card will have to pay for checked bags.