Buy each type of item from merchants.

You must buy one of every item type, from any number of merchants. They don't need to be any particular item quality, and you can sell them back after you've bought them. As with other challenges, you can also do this across multiple characters.

Sword
Mojo
Belt
Bow
Ceremonial Knife
Daibo
Dagger
Fist Weapon
1-Handed Crossbow
Leg Armor
Wizard Source
Quiver
Shield
Spear
Staff
Mace
Amulet
Boots
Bracers
Chest Armor
Crossbow
Dye
Gloves
Helm
Mighty Weapon
Polearm
Ring
Shoulder Armor
Spirit Stone
Wand