You get a companion named [npc=170046], who will sometimes dig up interesting items after combat.
He also sometimes grants you a special ability button that summons a giant by your side to help you in combat.
When he dug up something, he says: "Dredged up somethin' interesting over here, boss." so look for this text to appear.
Then you can click the sparkly little mud mount for some loot.
I am not sure if he's the only companion who does this, since this is my first playthrough, but thought I'd share. Free stuff!
He dug up all of this for me in one Bastion session:
- Potion of Spectral Agility
- Potion of the Psychopomp's Speed
- [item=171268]
- [item=116424] x5 or x6 (family type varies)
- [item=92683] (family type varies)
- Laestrite Skeleton Key
- Some food items
- And a bunch of grey items.
The companion stays with you for as long as you stay in the 'training grounds' (the whole of Bastion).
So you can run around and collect free stuff for as long as you like, it seems :)