HeavenShallBurn said:The thing is portable wealth=/= coinage
Coinage doesn't need to have even been invented for portable wealth to exist. All there needs to be is a relatively consistent idea of what Kind of things are valuable. Instead of finding a pile of coins in the dragons hoard they find a pile of gems, jewelry, and raw gold nuggets. When they arrive at the village the weary party is met by the local petty-king who calls them guest-friends. And they give him a gift of gems and swords found in the dragons lair and in return he gives them a gift of equivalent value. Wealth can be portable even without coins, it's transactions which are fundamentally different as they take on the mantle of an "equitable" potlatch as a means of establishing face.
That kind of reciprocal gifting works, but you don't choose which gift you receive.
What he said
At the core, it's about value and value is about an agreement on how the worth of things relate to one another. Even in a pure barter economy so long as a thing is considered to have value it can be traded for other things based on that perception of value. There will always be things of high value that are portable even if they aren't systematized in the same way as coinage. And we can easily use an abstract coinage value to track the value of these items in game terms.
In a PoL setting what would be high value and portable? The only things I can think of really are salt and maybe spices. There would also be nearly nothing to buy, as the kind of population density we're talking about dosen't generate the kind of surplus required. In this context, there also isn't really trade on a wide scale (or even on a small scale), nearly everything is restricted to local production. This means that things don't have consistent values. Most of the time your gold and jewelry is literally valueless, as there's no one within a hundred miles who has any use for it.
Without the economy of at least antiquity to support you, it would be an adventure in itself to simply spend your loot, or to acquire metal armour, as your point of light can't really have the resources to create one.