DIY Solar Water Heater From Plastic Bottles - Make a solar water heater from a pile of plastic bottles and cartons. This is great for the environment as it frees up waste trash and if you decide to build one you could use old bottles or what ever you have available.
Ranger evaporative cooling hat - slowly releases water to cool your head up to 20 degrees cooler than surrounding temps for up to 10 hours. Affordable and effective. Order a size larger than usual. Works better in hot, dry climates but still works well in more humid climates. Really nice on a bike ride since you generate your own breeze.