Clan Centurio and the Clan Hall
Side Quest

You can join Clan Centurio and enter the Clan Hall after you have completed the first Hunt in the game to defeat the Rogue Tomato. Speak to the Bangaa out front to gain access to the Clan Hall and then speak to Montblanc at the top of the stairs.

Vaan at the entrance to the Clan Hall
Montblanc

As you complete Hunts, either regular Hunts from the Notice Board or Elite Hunts provided to you by Montblanc, you will gain Clan Points and scale through the rankings. Attaining different ranks will allow you to purchase new items at the Clan Provisioner in the Muthru Bazaar in Rabanastre. The rankings are as follows:

Clan Ranks

Rank Marks Killed Montblanc's Reward Clan Provisioner
Moppet - 3 Potions Potions
Hedge Knight 2 2 Warp Motes
2 Teleport Stones
Hi-Potions
Rear Guard 4 3 Remedy
2 Teleport Stones
Gysahl Greens
Vanguard 8 3 Hi-Potions
2 Teleport Stones
Teleport Stones
Headhunter 10 2 Ether
2 Teleport Stones
Reverse Magick
Nihopalaoa
Ward of Justice 12 2 X-Potions
2 Teleport Stones
Bubble Magick
Brave Companion 14 2 Hi-Ether
3 Teleport Stones
Faith Magick
Riskbreaker 16 2 Elixirs
3 Teleport Stones
Bravery Magick
Bubble Belt
Paragon of Justice 24 3 High Arcana
3 Teleport Stones
Warp Motes
High Guardian 28 Empyreal Soul
3 Teleport Stones
Cat-ear Hood
Knight of the Round 32 2 Megalixir
3 Teleport Stones
Knot of Rust
Order of Ambrosia 45 Centurio Hero’s Badge
3 Teleport Stones
Dark Matter

Potions can only be purchased when you are on the Moppet rank and Hi-Potions can only be purchased when you are the Hedge Knight rank. For some reason, Bubble Belts cannot be purchased when you jump to the Paragon of Justice rank but reappear when you are a High Guardian or Higher. Aside from those three items, you can purchase everything listed in the ranks below the one that you currently hold.

Montblanc’s Rewards

Montblanc also hands out a number of rewards for defeating mini-bosses during your travels. These rewards are listed below:

Boss or Mini-Boss Reward
Four Flans 150 gil
Firemane 200 gil
Mimic Queen 300 gil
Demon Wall (optional) 1,200 gil, Warp Mote
Demon Wall 600 gil, Nugget of Electrum
Elder Wyrm 800 gil
Tiamat 900 gil
Vinuskar 1,100 gil
Earth Tyrant 1,200 gil
King Bomb 1,300 gil, Mallet
Ahriman 1,600 gil
Mandragoras 1,600 gil
Rafflesia 1,800 gil
Daedalus 1,900 gil
Tyrant 1,900 gil
Hydro 2,000 gil
Humbaba Mistant 2,100 gil
Fury 2,100 gil, Bacchus's Wine
Hell Wyrm 50,000 gil

He also provides rewards for controlling Espers, both the optional and mandatory ones that you obtain through the story:

Espers Reward
1 2 Arcana
2 Teleport Stone
4 High Arcana
2 Teleport Stone
8 Gemsteel
2 Teleport Stone
13 Serpentarius
2 Teleport Stone