From Guild Wars 2 Wiki
Dynamic Events. Most commonly, an NPC will request from any players in the area to collect certain items form a clearly marked area on the map, and bring them back to him. Once the NPC has enough items, he will generally run back and make something with them, such as a new environmental weapon, food or other item, and offer the item for sale. Those items are generally only available for sale for a few minutes after the event ends.Event Items are items needed to complete certain
They very rarely have any value outside the event, or can be sold by merely 1 copper, so they can be destroyed or sold if possible without consequence.