Speaking of
Disguise; I highly recommend it when pickpocketing as well because you cannot lose attitude if you're caught, especially if you also end up in combat (-45 attitude) which causes them not to talk anymore.
So a simple
Disguise with
Invisibility at the ready (either potion or spell) are essential (on Honour Mode at least) if you plan on pickpocketing anything without risk of apocalyptic chaos emerging. Saved my pickpocketing shenanigans on Honour Mode a ton of times because Lann Tarv (Bugbear merchant) in Moonrise kept catching a random halfling constantly trying to pickpocket a certain
[Dwarven Splintmail] from him

And yup, using
Speak With Dead on enemies who refuse to talk has a ton of interesting stuff and secrets to reveal. A bit tedious sometimes to always be disguising one self (I wish Larian would just forego that silly restriction), but worth it imo. For me
Speak With Dead,
Disguise and
Speak With Animals are essential utilities in every playthrough.
Level 1 Bard provides the latter two for free, while
[Necromancy Of Thay] provides speaking to the dead for free. I kinda wish there was a Druid in the Grove that could teach the player speak with animals, like Alfira can teach how to play an instrument.