I got home from my trip a few days ago. It was definitely hot, but we managed ok. We took Gatorade G2 packets to add into the water that was provided.
If you think that you'll want to go horseback riding or ATVing at Moab, then you'll need to pack some pants. Most of our group did the horsebacking. My family and a couple of other people chose to do the ATVs. I highly, highly, highly recommend it! It was the most fun we had our entire trip!
Our favorite meal was one that we booked on our own. We ate at El Tovar in Sedona (it's part of the resort...you'll eat breakfast there), and it was absolutely delicious.
We did end up wearing jackets in the evenings at the Grand Canyon. If you don't want to pack one, then they have a nice light green windbreaker for women that was only $23 in the gift shops. I took a jacket, but I bought one there too! The prices for shopping at the Grand Canyon were pretty good. Also, when you go to Monument Valley you'll have a chance to get some jewelry from the Navajos. A lot of it was marked prices like '$3.00 each or 4/$10.' Have cash available for this day.
Make sure you pack bandanas for the Jeep tour and the Monument Valley tour. They are $1.00 at Wal-mart, but around $3.00 and more at gift shops on the trip.