So they already make biodegradable coffee cups. What I'm thinking is that Starbucks and all the coffee companies like it should switch to biodegradable cups. Obviously, this will cost a bit more and therefore a cup of coffee will cost more... but if my plan works out, then the customers will be able to get the money they spend on the biodegradable cup back.
The coffee companies should team up with companies that sell plants (maybe some of the bigger hardware store chains that also have a gardening section) and tell people that if they bring their coffee cups to the gardening store they will get a deposit back for each cup.
Then the gardening store can reuse them to plant seedlings, and people can put them right into the ground when they get home because the cup will break apart as the plant grows.