Spell/Ability items are the items equipped in your left hand. They serve to augment and supplement your right handed combat equipment. The abilities housed in the items can be quick and immediate, like a palm blast. They can serve as a support effect like Bandages curing bleed, or Lucky Rabbit Foot increasing unit speed. Or they can be more spellcasting oriented, with casting charge times, powerful effects, vivid particles, and a long commit to yield the effect.
Because items have their singular effect and can be easily swapped with the quick equip wheel. They are meant to be unique, striking, and potent in their effects. With a broad enough ability pool, we can disperse different quantities of ability items in different biomes making regions significant for the powers you can access on a regional basis.
For example: You may find a flame blast ability from a “Everburn Root” at the base of a volcano. This region may be the only place you can find the item naturally occurring, the only other places being treasure rewards. This makes a journey (crawl) to the Volcano an essential step if you’re planning to go to the overgrown woods, which has frequent brush obstacles that take burn damage to break through. This enables situational unlocks of overgrown chests, or door passages covered in dry brush.
Lastly, Ability items are one of two classes. Items whos durability is consumed as cost of the spell, and cannot be repaired. These are most indicative of consumable Ability Items like the Lucky Rabbits Foot. Secondly is the ability equipment class, where durability may be lightly spent but instead the spell costs essence to cast. This is tied to major quest rewards and treasures, like the Blessed Elk Horn Pipe granted for completing Elder Elks quest line.
The equipment ability items are meant to last long periods and serve as an inventory capacity challenge as well as essence management challenge. While consumable ability items are meant to represent scarcity and passing availability.