Thaumcraft Treasure Bags

The mod Thaumcraft adds three treasure bags: Common Treasure, Uncommon Treasure, and Rare Treasure. They are obtained primarily by killing Thaumcraft's champion mobs. Right-clicking opens them, which gives a variety of Vanilla and Thaumcraft-related Loot.

Obtaining Treasure Bags
The primary source of treasure bags is by killing champion mobs. Treasure bags are a player-only kill, though some fake players (most notably Dynamism Tablets) can still get them. A treasure bag is guaranteed to drop, and the chances of getting each treasure type are determined by the looting level of the weapon used to kill the mob.

Note that Looting IV and above can only be obtained with non-vanilla methods.

Besides killing champion mobs, Kobolds from The Twilight Forest drop common treasures, and Thaumcraft bosses drop rare treasures.

Loot
When the bag is opened, Thaumcraft generates loot through a multi-step process, and spawns all the items in the player's foot.

Thaumcraft generates between 8 and 12 "loot items" whenever a bag is opened, regardless of its rarity. For common treasure, all loot items are drawn from the weighted loot table below. Uncommon and rare treasures also draw items from the loot table, but uncommon treasures have a 2.5% chance of dropping gear instead, and rare treasures have a 5% chance of dropping gear instead. The gear loot table is described below.

Generating Gear
Uncommon treasures have 2.5% of chance of dropping gear instead of drops from the table above, and rare treasures have 5% of chance of dropping gear. Dropped gear follows a different distribution. The type of gear (either a helmet, chestplate, leggings, boots, or weapon) is chosen with equal probability, and the specific item is chosen with the following weighted distribution. The gear will be damaged by up to 1/6 of its maximum durability. Gear from uncommon treasure bags have 25% of chance of being enchanted (using a random enchantability between 5 and 18.5), and gear from rare treasure bags have 50% of chance of being enchanted (using a random enchantability between 5 and 32).