OOOOH! THERE COULD BE RULES FOR CURRENCY SIMULATION!
Not the whole economy, because that’s usually not needed, but just a few things that the adventurers might experience that signify what’s going on in the larger world.
E.g. Kingdoms short on cash but high on ambition might start to dilute the gold content of their currency in order to raise funds for large projects (like wars). You can check the gold content of a coin by rubbing it against a touchstone and comparing the mark it leaves to a that of a trusted sample. If adventurers arrive in town and find that people prefer to be paid in foreign/older coins, that’s a sign that war may be on the horizon.