110~115 isn't unheard of around here. You pretty much get used to it. I have a full mesh jacket and NEVER ride without it, EVER. I also wear 6" boots and double chapped jeans with Kevlar, hip/knee pads.
I have a CamelBac 2L backpack. On the hot days, I can chill the water and 2L is plenty for most days.
A cotton/poly blend T shirt helps cool things, I got some at WalMart that are supposed to be cooler, I think it's just that they add a lot of poly to the blend.
Leather doesn't help you breathe at all.