Ever hear of cool ties. they have water absorbant beads in them that hold water for many hours.
They chill you to the bone when you first put them on, especially if you have themin the refrigator.
The military use them in Iraq for those that are overcome by the heat.
You can buy them in some stores, or make your own. I make them and send in care boxes to military.
http://www.watersorb.com/polymer_cool_neck_bands.htm