For the Nightfall Salvage Item of the same name, see Stolen Goods (Salvage Item).
The Stolen Goods are merchandise that the bandits stole from Gelsan the Outfitter. They supposedly contain the Vanguard Equipment that Captain Arne wants from the outfitter. Gelsan asks players to return them to him as part of the quest Vanguard Equipment.
Note that the Stolen Goods are a "Bundle" (i.e. an object that does not go into the inventory, but has to be carried in one's hands).