The Item: Polished Obsidian Shards.
Why: Rare, beautiful, and dangerous. These shards are harvested from the high-risk thermal vents on Fire Peak. They are the only material sharp enough to bypass the "Ban on Iron" for surgical or hunting purposes.
Exchange: High-tier items like medicine from @Amara Jallow or "Old World" relics.
The Item: Salvaged Hull Rivets or Machine Washers.
Why: Because of the Third Pillar (No Hand Shall Hold the Iron), metal is the ultimate forbidden commodity. It is heavy, durable, and represents power. The Iron Guard uses these to pay for information, while rebels use them to craft illegal tools.
Exchange: Mid-tier gear like leather armor, specialized rations, or passage across the channel.
The Item: Dried Sulfur "Nuggets."
Why: Abundant near the vents but vital for daily life. These are used for starting fires, keeping the "Sulfur Flying Foxes" away from camps, and—secretly—by @Saren Lundie to create primitive explosives.
Exchange: Basic necessities like clean water, dry kindling, or a seat at the Ember Circle.