At my new job, we have free beverages at a vending machine that dispenses plastic cups for every one you take (including water). You'd walk around and you would normally see 4 or 5 empty ones on everyone's desk.. I thought it was extremely wasteful. Started off by just reusing the same cup by putting it in the slot before choosing a drink but sometimes that would jam the machine, so I promptly stopped.
After the second jam, I spoke to the repair woman who told me that it actually recognises weight, so even though the small plastic cup won't work, a mug or a bottle will trigger the no-cup function, great! Bought myself a fancy Marvel thermos bottle and not only can I put two drinks instead of one, but now a bunch of other people have followed my lead! And it's a great convo starter!