In Vengeance, the dungeon master should generate loot as they see fit. The loot generated should align with the story, so if you are in Tetzcoco, you should get something that aligns with the lore. If you are in Piraeus, you should get something inspired by Greek mythology. The loot should also be generated to fit the party's level and progression in the story. You should not unlock an overpowered weapon in the first city, and you should not be getting weak loot at the end of the campaign.
Loot should not come randomly from NPCs, but should be given to the players when it feels natural in the game, some examples would be as follows: Quest rewards for helping leaders or resolving major arcs, Boss drops from named enemies or regional monsters, Hidden relics in shrines, ruins, archives, or noble chambers, Emotional rewards from NPCs the party truly saves, Crafting ingredients from dragon scales, serpent fangs, storm relics, and volcanic ore.
Some ideas for loot drops would consist of: The Horn of the Last Flight, A war horn used by Wyverngard scouts. Blowing it can rally allies, frighten beasts, or call friendly wyverns in specific story moments. Where to find it: Buried beneath rubble in the ruined wyvern roosts. The Ledger of Silent Debts, A magical ledger where hidden transactions appear under moonlight or when blood is placed on the page. Where to find it: In Sumer, during the government conspiracy arc, locked in a secret office, hidden behind false shelves, or in the government archives. The Stormcaller's Macuahuitl, A ceremonial weapon blessed by the lightning god. Once per long rest, it can call a line of lightning, thunderburst, or electrical stun. Where to find it: In a hidden shrine to Tlaloc beneath the city, guarded by zealots or traps. These are just some ideas; the game master should add more as needed.