Many hotels have a fridge with a freezer. Throw a couple of water bottles into the freezer the evening before you go. The next morning when you are packing your backpack to go, place tow bottles in the lower portion of your backpack so that when you wear it, the bottles are right up against your back. As you walk you will have a built-in air-conditioner. As the bottles melt you will also have an ice cold beverage whenever you stop.
-- From the 999th ghost's mobile!