I've been having some serious issues overheating on long rides (70+ miles). What I'd like to find is some sort of neck wrap that you can fill with ice cubes. The ones that come with cooling gels that you have to freeze first will do me no good, as my overheating problems happen after 4+ hours of riding. I've done a number of amazon, internet, and forum searches, but can't seem to find anything that's refillable (which I could do at a convenience store stop).
In the meantime, I'm going to try slipping a few ice cubes into my sun sleeves and socks. I imagine they'll melt pretty much immediately, so a larger repository of ice would work a lot better. I've learned that once I start overheating, it takes a lot to reverse the process to the point I can keep riding safely.