the issue is things in a bag don't exist as far as game code goes so you would have to take them all out to try one by one at each lock
this [doesn't exist] is part of the base code in every Larian game and has all sorts of bugs/ cheats linked to it
No this is incorrect currently. I just re-tested this to confirm. Currently if you have a key stored in a pouch you can unlock a chest or door just by having your character try to open it. It is not necessary to open the pouch or remove the key from the pouch beforehand. After you open the chest or door the key will remain in the pouch. If a party member who does not possess the pouch attempts to open the chest or door then the "magic pockets" kicks in. Again it is not necessary to remove the key from the pouch, but in this case after the chest or door is open the key will be in the possession of the party member who opened the chest or door and is no longer in the pouch.
So a pouch will currently act as a "keyring" of sorts though who is to say if the functionality will remain on final release.
Also you can directly drink potions stored in a pouch by opening the pouch and selecting it or if you have the potions in the pouch but also attached to the hotbar you can drink them from the hotbar without opening the pouch.
Whether all pouches have this functionality I cannot say as I didn't test them all. Any I have found and used do work however. The one I used for the test today is the one found with the spider egg contained within.