I took a page from vakkotaur's book, sort of: I have a half-gallon Coleman jug which I filled halfway with ice, then all the way with water before leaving. I sipped at that all day, and it does seem that hydration makes long drives much more tolerable.
I'm going to get on the road about the same time, or maybe a little later, tomorrow. I'll be passing through Oklahoma City and Dallas in between rush hours that way, which is a Good Thing. I'll probably get to the hotel in Houston about 6 PM, and don't plan to do much of anything there that evening, as I'll probably be thoroughly wasted.