i think we all remember when in the avatar state, as a parting gift, master pakku gave katara a vile with water from the spirit oasis which according to master pakku, had special properties. They have to lead on with that plot, avatar has done a great job of not leading us to dead ends. it was a necklace if i remeber correctly, but katara doesnt seem to be wearing it. (however it might have been a long string) it has to come in handy. maybe aang will die from a major injury??but katara can use it as healing water to bring him back to life
WHO KNWS!