Thank everyone for the ideas and advice. I'll be up in the Q end of August so I have a mix of fairly warm days and cooler nights, sometimes very cold indeed. I like both the sink method and the chem pack method.

A side note on the sinking, when filtering water to drink I have a 30' hose extension for my purifier. Attached to it is a 2 ounce fishing weight that brings it down. I can get water thats pretty darned cold for adult beverages or a near ice cold gatorade.   It doesn't stay cold for long, but it sure is nice when its really hot out and the route was portage heavy.