To unlock the Yoink achievement in Far Cry New Dawn, you must successfully loot a Highwaymen Supply Drop. The Highwaymen supply drops will be randomly dropped on the map by an aeroplane.
You will be able to identify them by the yellow smoke coming from them and the red marker. When you find one, a group of enemies will attempt to defend it. Once you have defeated them, approach the supply drop and hold the X button to loot it.
Once you have looted the supply drop, the Yoink achievement will unlock.