KeepCups are reusable coffee-cups with a little plug that you lift, slide to the side and snap in-place, enabling the drinker to indulge without risk. It works like this, which is a lot easier than it looks if the user has two hands ((I.e. not using one of them to hold the friggin' camera.)) available...

Drop Coffee have put them out on sale today! Or if you want, you can design your own cup at the supplier's.

Sustainability rules.