Friend of the Crew Achievement
Find the guitar and teddy bear on the VOLGA level.
Before you head out to find Krest’s railcar, talk to Nastya and your squadmates regarding their Teddy Bear and a guitar respectively. They will each give you a location to find those items, and there will be special icons on the map for them. Go to each location and retrieve the items.
As the achievement suggests, you only need to find these items, you don’t actually need to take them back to the requester. Though… you still should.