Coin

Beyond Vouchers the people of Styx still use coins as currency no matter how much the Temple Parliament forbids it.
These coins are:

Stygian Kharon, usally called Kharon (gold).

Stygian Serpents, usually called Serps (silver).

Stygian Petterlings, usually called Petties (copper).

1 Kharon equals 10 Serps equals 100 Petties.

There are also commemorary coins with special minting to celebrate the anniversary of the Great Revolution, the ones for the 100th are worth the most but ones minted for the 300th still go for over 100 Kharon a coin.