This is all kinda off the top of my head (and in part because I somewhat dislike the whole mass-alt crafting writ method of acquiring upgrade materials).
- Unlocking any Chest has a small chance to spawn an "Enraged Looter" mini-boss. Drops a "Looter's Pouch", with rewards as though searching a Master Chest.
- Harvesting any node has a small chance to spawn an "Enraged" Leather source animal unique to the zone, as a min-boss, that drops a "Fibrous Bundle", that contains a variety of Leather/Weaving crafting mats.
- Any Leather source animal has a small chance to drop an "Undigested Pouch", that can provide a variety of Alchemical Reagents.
- Delve bosses have a moderate chance of dropping a "Looter's Pouch", on cooldown.
- Public Dungeon Bosses have a high chance of dropping a "Looter's Pouch", on cooldown.
- World Bosses drop an "Adventurer's Pack", on cooldown, that contain valuable items, Possibly even Gold quality standard items (deconstruction).
- Dolmens drop "Cultist's Coffer"/the reward chest contains more soul gems/enchanting materials (chance even to get Kuta)
- From all of these a small chance at zone-specific housing furnishings, unbound.