Save a tree - Get coffee mug filled for free at Starbucks on Earth Day Published April 21, 2011 By 95th Air Base Wing Public Affairs EDWARDS AIR FORCE BASE. Calif. -- In the spirit of Earth Day, the Edwards Air Force Base Starbucks location is offering a free cup of coffee to all those who bring in their own coffee mug on Apr. 22. Additionally, the store will offer a 20-percent discount to anyone who wants to purchase a Starbucks travel mug on Apr. 22.