Depends on your activity level, I guess.
I think Wikipedia covers dehydration and starvation quite thoroughly.
With dehydration, you start to hallucinate and eventually your kidneys fail as they are the main biological pathway for water. Then your heart fails due to hypervolemia and toxemia from the kidneys stopping.
Starvation... I've heard you just eventually slip into a sort of lethargic apathy until you suffer organ failure. By the time you die your mind is not able to process very much information. Eventually the pathways for protein synthesis, which in of themselves are made of protein, break down, and then there's no going back. AFAIK it's why really starved children and adults can't be resuscitated.