Now where to spend it...

Coupons can be obtained from the Awesome Sink, which is a craftable building.

Once built and powered, use a belt to feed any excess materials you don't want any more from a storage container into the Awesome Sink. It will consume them, and produce tokens in return. Interact with the building, print the tokens and then (the non-obvious bit) drag the printed coupon at the bottom of the screen into your inventory.

You'll need coupons for Are you sure that's coffee?, Do you need that? and No refunds.