I do a lot of hiking here in Texas where the weather is about the same. You've already gotten some great advice so I will just reiterate one point that I feel is of 'grave' importantance based on my own hiking experience in 100+ degree weather. Water, water and more water. <img src="/images/graemlins/grin.gif" alt="" /> Carry as much water as you can (be reasonable of course) and have multiple methods for purifying (filters and chemicals) and carrying (carry ziplock bags as backup to your primary storage method) on the spot! Never ever get too low on water! The only other thing I'd add to what has already been said is get a good wide brim, light colored hat like a boonie hat.