Winn-Dixie Stores Inc. plans to offer flu vaccinations on a walk-in basis and through vaccine clinics at all of its in-store pharmacies beginning Sept. 1. Customers using their Winn-Dixie Customer Reward Card will receive a $5 discount off the $28 flu vaccine ($23 with the Customer Reward Card). Winn-Dixie’s pharmacies also are offering a new,…