Are all of the containers in the game safe for storage (RE IWD)? I've used some in the Promenade and the sewers to store items I didnt want to sell just yet and hope not to lose

I believe that all containers are safe. The only place items will 'disappear' is on the ground. I am using a chest in Nalia's keep and nothing has disappeared from there, so I think you can store items in any chest,table,barrel,etc.....and they will remain there.

nt

There are exceptions to this safety
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Some places are 'cleansed' by the game at points relevant to the plot. For example, when as a fighter, you get the keep as a stronghold, or as a ranger you inherit the cabin, in these cases, the games tidies/resets the location. Otherwise, I've never had anything disappear from a container.

Only problem I had is if you upgrade the game and uses an old save the game can crash..