They provide the Coke and you provide a glass. Sounds efficient for me. That's how I usually handle it, when buying beverages.
You can get old used Superfest glasses on ebay for 10$ per piece. That's sustainable capitalism: they don't get thrown away and the seller makes a great price.
Plus: you can get the original DDR/GDR design from 30 years ago and fill it with any beverage you want.