It's totally not what people watch these movies for and would be terrible for everyone save me, but I'd love to see more exploration of the whole alternative economy they have going with the gold coins. In my head-cannon, the fiat money that we all use, that the ordinary world knows, is just for the outside people. The people in the know, those part of the world of real power, never went off the gold standard and Bretton Woods and Nixon was just a means to fob off the masses and hide away the real movers and shakers and power. The assassins bump off politicians and businessmen and warlords who stick their nose where it's not wanted or who break free. And the gold is the currency the true assassins (descended from the original hashisim) have always been paid in. Hence that Arab dude in part three. Anything really meaningful - contracts, information, new identities, safety - it's all paid for with the gold and the fiat currencies are just created and handed around as needed.
Wait... we're still talking about a movie, right?