Crystal Caravanners are groups of adventurers in Final Fantasy Crystal Chronicles. Their purpose is to gather Myrrh for their town or kingdoms Crystal each year, in order to repel the poisonous Miasma.

The shattered crystal's shards warded off miasma, but they still needed the water. Thus began the journey of the crystal caravan.
Carbuncle

Crystal Caravanners journeys began after the arrival of the Meteor Parasite that spread Miasma across the world. Crystals were the only thing able to repeal the poisonous mist, but the effect would only last for about a year before it needed Myrrh to replenish its effect to ward off Miasma.

So each town and settlement would send off groups of adventurers in Caravans, to collect Myrrh drops from Myrrh trees found within dungeons. With them they would take the Crystal Chalice, which was not only used to collect the Myrrh drops but protect the Caravanners from the Miasma.