Mimics...now THAT would be a legit justification for all the empty containers found in the game....not only are Mind Flayers trying to take over the Realms, but Mimics have had a population explosion and trying to take over as well!!!
Perhaps thats the real reason they put barrels everywhere? They are trying to get us used to shooting barrels for an easy win, but in the full game there will be clusters of barrel mimics you dont want to aggro. :0