4) Spray Skirt
That is the minimum requirment. Without all these you cannot paddle, or should not anyway.
After that there are only a few things you will need and a score of things you don't need.
Throw rope, Dry Suit, dry top or wet suit or any combination that works. Poggies, Booties, First Aid kit, Pin Kit, A vehicle helps and you will need THE ATTITUDE!
Welcome to the wacky world of whitwater paddling!