Apart from going maximum Dexterity, the utilities I recommend having are;

  • Always Disguise yourself first because then you won't lose attitude if you're caught stealing.
  • Always enter Turn-based Mode if you plan on stealing more than one item at once.
  • Have [Potions of Invisibility] or Invisibility at the ready so that NPCs who temporarily become hostile if you're caught will abandon pursuit immediately.
  • [Arrows Of Darkness], Darkness or Fog are essential if the target you plan to steal from is visible by a ton of NPCs from a ton of angles (don't drop it on top of them, but slightly next to them).

Equipment;

  • Save the [Gloves Of Power] from the Grove's introductory battle as these will become essential later.
  • [Silver Pendant] is a free Guidance amulet if one is not playing a Cleric or using Shadowheart.
  • [Smuggler's Ring] is essential and will be with you forever.
  • [Gloves Of Thievery] will be the main early-game gloves for pickpocketing, until you meet Lady Esther in the Mountain Pass.
  • [Cat's Graceful Cloth] obtained from Lady Esther is an essential piece and after obtaining it the [Gloves Of Power] also become an essential piece.
  • [The Mirror Of Loss] in ACT 3 allows you to increase your Dexterity by +2 (maximum 22).
  • [Shapeshifter's Boon Ring] obtained from the Ox although claims it gives 1d4 to all checks while Disguised, does not work for pickpocketing (it's bugged).

Extra helpful tips & bonuses for stealing high-risk items (especially on Honour Mode);

  • Guidance (1d4) is available from an amulet or from Shadowheart since she's a Cleric
  • Bardic Inspiration (1d6) is available by multiclassing anyone into Bard (I like to give Shadowheart 1 level in Bard because it's incredibly helpful)
  • Bolstering Magic: Boon (1d4) is available from Karlach as a Wild Magic Barbarian

With this you will accomplish +17 into Sleight Of Hand, with the minimum roll being 19. The highest I ever rolled was 47 and the chances of failing a pickpocket are nigh impossible unless your dice really have a thing against you, like they sometimes do against me;

[Linked Image from i.imgur.com]

On top of all this I recommend placing the pickpocketing equipment in the Custom hotbar for quick-'n-easy access when wanting to indulge in pickpocketing shenanigans;

[Linked Image from i.imgur.com]

As for which targets to pickpocket, anyone and everyone for whatever you want or need.

I personally never give vendors a single penny, I just steal their every single unique item and whichever consumable I think I may need (usually darkness arrows, invisibility potions). Other NPCs which may have something great that can't be pickpocketed, like Kagha's unique [Broodmother's Revenge] necklace, I knock-out while Disguised. No unique shall be left in the hands of peasants!

Hopefully some of this helps. enjoy your five-finger discounts grin