We recently invested in two Camelbak MULEs for use while hiking around the Arizona desert in search of caches. They provide a ton of water, as well as space for REI's ultralight first aid kit, spare batteries, trail food, and some other important stuff. The other thing I like is strapping the 2-meter handheld into the mesh on the back, looping the speaker mic through the rings and down the shoulder strap opposite the tube. That leaves both my water and my HT within reach, just in case.
I also invested in better shoes for hiking the desert, as well as a lightweight pair of cargo shorts to haul around extra stuff. It's convenient to have a pocket to slip the GPSr into before climbing up a rock face. I also love the moisture wicking t-shirts and socks. After one recent five mile trek through the desert in 100 degree heat, my t-shirt and feet were bone dry.
Take care.
