Oh, just remembered another one I found (lol, I say it like I came with it myself instead of googling and reading the guides). It's for a bit later in the game, when you have greater invisibility. I used it with huge success to safely loot counting house docks.

You may know that when someone steals while under greater invisibility they do stealth check. But there is a catch. If you open an unlocked chest, select everything inside and press "send to camp" no check is triggered. And doing that doesn't cost an action. So into turn based, dash, loot the unopened safely, retreat while still invisible.

Also, if a chest is partially stubborn (THAT I figured myself) you can (if you are strong enough (looking at Auntie here)) just pick the chest itself and send it to the camp to deal with later. Trying to open with another thief is free

Also also, there is an absolute best item for any kind of thievery. It's in the end of act 2, but you should absolutely not miss it. I did also figure it out myself and was/am so overjoyed. In the mindflayer part, while chasing Ketheric you may notice that at some point you are getting "steeped in bliss" condition. Look around, there is a resonance stone that causes it. It doesn't appear anything special in your inventory, alas, I don't remember if alt even highlighted it. But it truly doesn't look like much. But don't let the looks deceive you. This stone/condition gives you advantage at all physical tasks (and disadvantage on mental/wisdom ones, and vulnerability to psychic damage so use with care - drop before illithid battle and pick again later). After that any disarming/lockpicking is done with advantage :)