Pick up a FREE Mtn Dew Overdrive at Casey's General Store today as part of their FREE Offers Daily with 24 Days of Casey's Rewards! Includes a 20 ounce beverage. Limit one per member, while supplies last. Find this in Offers under the 'Rewards' section. Save offer in the Casey's app or online to redeem in-store. You must be a Casey's Rewards member (free to join) to get this freebie. As a Rewards member, you'll earn points on all your Casey's purchases – in-store, online, or at the pump.