Rogue Galaxy Quarry: The Cave Bandit
The Cave Bandit can be found in the extremely large room which is just past the room you fought Gale in on this planet. The ? you'll want to use the Stella Crystal at is in the center of the room by where the stairs lead up to the central platform. The boss fight is a total pain in the ass the guy hits like a tank and has massively high defense. The only upside is his attacks are extremely slow and extremely predictable.
I recommend hanging back and shooting him as much as you can before your gun runs out then you'll want to spam Flash Sword and whittle him down the best you can. I tried spamming my other abilities on this guy but they just seemed ineffective. Also something to keep in mind is that none of the quarries in Rogue Galaxy consume the item required to summon them.
That's why I recommend you try and keep at least one of all items that are required in the Revelation Flow on you. Some of the quarries require items not used in the Revelation flow which are usually acquired by some other means on the same planet as the quarry. More information for those quarries are found in their select guides.
After you defeat The Cave Bandit explore the room a bit, specifically check behind the large rock in the room for a chest. You won't regret it!
The item required to summon this boss is a Stella Crystal. If you are missing the item required to summon this boss grind some battles and cross your fingers or go treasure chest hunting on a planet you've 100% the map on. In Rogue Galaxy once you pass a certain chapter the loot table of items that can drop for you ingame is updated.
What I mean is, every item has a chance of dropping off every creature after you've passed that chapter that allows that item to drop. At least this is how it works in my experience. Therefore, if you're missing any items to summon any of the quarry bosses all you need to do is grind a little until you get that item to drop for you. Good luck!