The bone and coin piles scattered around can be interacted with. When the player does this Collectables will appear and they can grab them. These are all "Collectable Containers" that we used in Doodle Safari and can be read about here: Collectable Container
The chest at the end is very similar except we have extended it into a "Locked Collectable Container". This lets you remove a number of Collectables from the player when they open it, in our case a single key.