I get the Shot blocks that have extra salt (I think they're the margarita flavor) since my diet isn't terribly high-salt and I seem to lose more of it than normal people. 40 miles is about the point where I need additional real food too.

If it's really warm, I take the Camelbak and fill up the second bottle with diluted Gatorade. I like the sound of Gu Brew, though.