[kawsper]

Coffeeshops (Costa and Starbucks) in the UK offers a 25p discount if you bring your own cup.

Just be aware that there are some strange terms and conditions: Costa requires you to have a lid, or else they can refuse to use it, the rule seems bizarre since they will happily fill your coffee in a lidless ceramic mug, but if you bring a lidless metal thermo mug like mine it is a no-go: https://www.snowpeak.com/collections/mugs/products/ti-double...

[alecst]

It's definitely better than nothing, but sadly this has a very small effect on consumer behavior. This was the main thrust of my presentation.

My proposal was to change the way this "discount" is realized -- by giving everyone the discount, and then only charging people who buy the cups.