You'll need more water and food than you think.
My wife and I hiked to Upper Yosemite Falls on June 12, 2010. We have been training for this hike for months and doing alot of research. We took 4 liters of water each along with Cliff Bars, apples, nuts, PB&J etc. I am 62 and my wife is 47. I drank 2 liters on the way up aong with 2 cliff bars and some nuts and raisns. I rested several times on the way up and finally, after much effort, made it to the top. We had lunch and then it happened. I started getting dizzy, nauseous and getting leg cramps in my inner thigh. I was in major pain with the cramps and could not stand up. I could not make it down in this condition. As chance would have it, there were 3 REI guides with a group there and they were trained as First Responders in medical emergencys. I was dehydrated. After about an hour the symptoms went away and I was able to hike down to the valley floor. It took us 4 hours and 45 minutes to get to the top and 4 hours to get down. WARNING !! I drank 2 liters of water going up and still got dehydrated. The REI Guides refilled my Camelback on top and I used it all on the way down. If you plan on making this hike take MORE water than you think you'll need. All the water you can carry unless you carry a filter or water purifiying tablets. If the guides hadn't filled my Camelback I would have gotten dehydrated on the way down. Other than that, it's a wonderfull, very strenious hike. Be prepaired.