1. Generally interesting steals in each continent area.

2. Bosses you want to reload for if you fail to steal things from.

3. Thief's Gear to keep a look out for!

4. Dungeon's stealables(Will be done later)

As a little side note I intend to make my Thief the character with the highest preemptive and agility so he goes first and has a higher chance to steal things. Just a clue as to how you may wish to build your thieves!

Items with * next to them are awesome to collect for preperations.
Also note this is prior to getting the Airship when the random encounters for the continents change for the most part.

1.Area Surrounding Oakwood: Tiny SP Orbs, Antidotes, and Sleeping Bags. Save you some cash early on.

2.Desert nearby Dry Gulch: Tonics, and Tiny SP Orbs.

3.Forest nearby Dry Gulch: Tiny SP Orbs, Antidotes, Sleeping Bags, and Holy Bombs.

4.Area around the Forest Tower: Tents, Ice Bombs, Antidotes.

5.Forest nearby Alfheim: Vocalizer Serum, Fire/Holy Bombs.

6.Areas surrounding Earth Caves and Doria: Vocalizer Serum, Smelling Salts, Tents.

7.Surface of the Sea: Thunderstorm Bombs, Thunder Bombs, Wind Bombs

8.Areas around Riverdale: Blaze Bombs, Holy Light Bombs, Hyper Wall Tonics, Tents, Small Magic Potions... Yeah go fishing!

9.Areas around Rubicon: Snowstorm Bombs*, Small Cottages, Hyper Ward Tonics.

10.Green areas around Gaia: Remedies*, Small SP Orbs, Thunderstorm Bombs, Hurricane Bombs, Hyper Vigor/Blitz Tonics.

11.Area around the Abandoned Lab: Holy Fire Bombs, Hellfire Bombs, Small SP Orbs, Hyper Mind/Ward Tonics, Hyper Suge/Bubble/Blitz/Wall Tonics, Hyper Jolt/Shock Tonics.

12.Area around Aunlak: Hellfire Bombs, Small Cottages, Hyper Tonics.

13.Areas around Igloo and Hermit's Tower: Small SP Orbs, Small Cottages, Hellfire Bombs, Remedies.

14.Far Eastern Continent: Small Cottages, Hyper Blitz/Wall/Vigor Tonics.

15.Desert around the Oasis: Remedies, Small Cottages, Holy Fire Bombs.

16.Area around Midgard: Remedies*, Small SP Orbs, Thunderstorm Bombs, Hurricane Bombs.

17.Areas around Lemuria and Moa Races: Small Cottages, Hyper Blitz/Wall/Vigor Tonics.

18.Areas in between Lemuria and Babel Citadel: Hurricane Bombs, Thunderstorm Bombs, Hyper Tonics.

19.Green Areas around Asgard: Remedies, Hyper Tonics, Hurricane Bombs, Thunderstorm Bombs,

20.North of Naiad Mountians:Hellfire Bombs, Small Cottages.

1.Midbosses:
Gorgon: Large SP Orb.
Baal: Thaumaturgical Ring, Mercurial Ring, Quicksilver Ring.
Seventh Circle Demon: Five Elemental Protection(aka Fire, etc) Rings.
General Hannibal: Repel Ring, Lure Ring.
Magi Guardian: Experince Ring, Midas' Ring, Thaumaturgical Ring, Quicksilver Ring.

2.Targets:
Goblin King: Warp Stone, Small Cottage.
Mutated Ghoul: Small SP Orb, Holy Light Bomb.
Dark Phoenix: Medium SP Orb, Small SP Orb.
Great Imp: Small SP Orb.
Sapphire Scorpion: Medium SP Orb, Small Cottage.
Amorphous Blob: Medium Cottage.
Rogue Knight: Medium Cottage.
Captain BlackBeard: Medium SP Orb, Small SP Orb.
Death Mage: Medium Cottage, Holy Light Bomb.
Great Snow Golem: Large SP Orb, Hellfire Bomb.
Loki: Large SP Orb.
Barbarian Brute: Large Cottage.
Mutated Behemoth: 3x Large Cottages.
Troll King: Large-Medium Cottages, Sonic Boom Bomb, Hellfire Bomb.
Anaconda: Large Cottage, Blizzard Bomb, Hellfire Bomb.
Mutated Serpent: Large Cottage, Large SP Orb.
Dracula: Large Cottage, 2x Holy Fire Bombs.
Giant Squid: Sonic Boom Bomb.

3.Bosses:
Giant Ogre: Might Ring, Medium-Tiny SP Orbs
Tower Guardian: Swift Ring, Rune Ring, Medium-Tiny SP Orbs.
Treant: Poison Ring, Small SP Orb.
Outpost Captain: Titanium Armor, Warp Stone.
Ifrit: Illusion Ring, Medium SP Orb, Full Potion.
Helios: Protect Ring.
Tainted Earth Spirit: Illusion Ring, Medium SP Orb, Full Potion.
Cyclops: Ogre Ring, Medium SP Orb, Full Potion.
Citadel Drone: Illusion Ring, Medium SP Orb, Full Potion.
Giant Ice Tiger: Ogre Ring, Medium SP Orb, Full Potion.
Nyx: 2x Leviathn, 2x Full Magic Potions, 2x Full Potions. Only Steal if you intend to use em. You dont get to keep them after leaving the Abyss!
Marsh Beast: Protect Ring, Poison Ring, Silence Ring, Paralysis Ring, Sleep Ring, Large SP Orb.
Desert Guardian: Bulwark Ring, Five Elemental Protection(aka Fire, etc) Rings.
Dark Lord: Full Magic Potion, Full Potion, Large SP Orb.
Kraken: Lure Ring, Skillful Ring, Large Cottage, 3x Full Potions.
Giant Ogre/Pirate Soul: Midas' Ring.
Tower Guardian/Treant Soul: Deserter's Boots.
Ifrit Soul: Renewing Hat, Healing Helm.
Marsh Beast Soul: 5 Status protection Rings
Desert Guardian Soul: Burgalary Ring, Illusion Ring, Ogre Ring, 2x Full Magic Potions, 3 Full Potions.
Helios Soul: Element Ring.
Dark Lord: 2x Leviathans.

4.Super Bosses:
Grotesque: Element Ring, Mercurial Ring, Quicksilver Ring, Repel Ring, Lure Ring.
Colossus: Experince Ring, Surge Ring, Bubble Ring, Ward Ring, Bullseye Ring.
Vanir Golem: Rainbow Robe, Rainbow Armor, Amaranthine Ring, Element Ring.
Kali: Kali's Ring, Amaranthine Ring, Vanir Sword.
Dark Lord: 2x Leviathans.

Generally you want agility boosting equipment over all other stats for your thief, for the best stealing results.

Also note that Ninja, the Thief Class Upgrade is caple of equipping Shields and Lances!
(Iron)Tough Breastplate:+40 HP +24 DEF +4 MGD +3 AGI
(Leather)Nimble Knife:+8 ATK +3 WGT +15 ACC +5 AGI
(Iron)Agile Helm:+11 DEF +8MGD +10 ACC +10 AGI
(Steel)Thug's Knife:+16 ATK +10 WGT +15 PRE +15 AGI
(Mythril)Fleet Knife:+27 ATK +12 WGT +20 PRE +20 AGI
(Crystal)Floating Sword:+49 Atk +22 WGT +25 PRE +25 AGI
(Crystal)Winged Armor:+120 HP +43 DEF +16 MGD +30 PRE +30 AGI
(Crystal)Hyper Helm:+28 DEF +24 MGD +25 PRE +30 AGI
(Crystal)Active Cloak:+28 DEF +24 MGD +20 PRE +20 AGI
(Dragon)Sky Shield:+42 DEF +14% CRI +30 PRE +30 AGI
(Diamond)Hermes' Lance:+43 ATK +8 WGT +70 PRE +35 AGI
Deserter's Boots:+20 DEF +150 AGI The highest Agility giving piece of equipment. Acquired from the sidequest given by the man on one of Doria's Piers.
Vanir Gauntlets:+50 ATK +60 DEF +100 ACC (2x EXP)!