I think there is an easy solution: More expensive (like USD 1) foldable cups, that are expensive enough that people will actually re-use them. In Sweden we hav

I think there is an easy solution: More expensive (like USD 1) foldable cups, that are expensive enough that people will actually re-use them. In Sweden we have a model I like a lot, which is a modern, foldable version of a traditional saami drinking vissel called "kåsa": https://www.dentakit.com/foldingcup.html https://www.dentakit.com/foldingcup.html They are often sold in hiking / outdoor shops etc. I'm sure someone could create a nice version suitable for take-away coffee.