What if potions and tonics had negative side effects? Potions of increased strength cause violent tempers, or damage joints. What if potions of dexterity caused tremors, or palsy?
What if they were addictive, and had withdrawal symptoms?
Could someone make a bad batch? No one use the brown strength potion!
A simple flag, faded by time and sun, tattered and worn by untold years flying from the pole of a bannerman, passing hands from officer to officer, from one generation to another. It is a humble symbol of great importance, and greater inspiration to those who see it. Soldiers become heros filled with espirit de corps, enemies loose their nerve and fire. It is not an enchanted item, but a powerful item still...
The PCs traveling along the road/path/trail begin to hear a low droning sound. As they approach they find their path obstructed by hundred of thousands of droning insects. Locusts swarm though the air, feasting on the grass and plants. Passage will be slowed, but the insects pose no threat to the party, aside from being crunchy and disgusting underfoot, climbing into pouches and eating exposed food goods.
Expansion from the Horse Brass item: Specific Armor charms.
Cooling Touch Charm: protects horse against extreme heat, and fire, magical and mundane
Jove's Favor: tin charm shaped by a lightning bolt that protects a horse primarily from natural lightning, but also potentially from lightning based attacks. In real life, lightning kills quite a few horses and cattle a year.
Hermes' Blessing: gold charm that grants the horse magic resistance, and perhaps immunity to cantrip level magics.
Vulcan's Steed: This large iron charm in epic fashion renders the steed invulnerable to iron weapons. Such things clatter off of the animal's hide like twigs.
Consider the idea of spontaneous genesis of life, as used to be belived. What strange kinds of life might arise from modern substances? What kind of vermin would a landfill produce, or an oil spill on the ocean?