Just did this for fun back around before POTC 2 DVD came out. Thought maybe readers might enjoy. Not gonna type a whole storyline. Just thoughts.
So POTC 2 was mainly about finding Davy Jone's heart to control the sea. That quest is over. POTC 3's main quest is getting Jack back and getting back the heart. There has been discussions about a possible ring plotline. Don't know if its significant. It's been rumored the Kraken would have a bigger role in POTC 3. Saw a concept art of a ship in a whirl pool in POTC 2 bonus feature. Also mentioned chupacabra and fountain of youth which I thought of before.
SO, Kraken can be summoned by Davy Jones to create a stormy weather which can create a whirlpook to Jones' locker.
Jack returns to the real world with the help of Barbossa and crew, but must drink from the Fountain of Youth to stay alive before it's too late. The fountain is guarded by packs of cupacabras (http://en.wikipedia.org/wiki/Chupacabra). Tying in with the ring subplot, the fountain only works with the ring worn or the ring in the cup and then drunk.
Tia Dalma sensed Jack would be in trouble and returns Barbossa from the dead before the island was submerged. Possible first 10 minutes of the film.
While in Jones' locker, Jack encounters Norrington's crew. The crew helps battle Jones' crew in the climax.
There should be a Jack vs Davy Jones sword fight. I saw a toy of this and thought it would be in the movie. NOT!
That's about it for now. Can't wait for POTC3
Turner releases his father from service, Lord Beckett looses his control over the seas, Jack meets his father, Chinese pirates help...