All good discussion here.  Living down south, we're typically greeted with substantially cooler temps than our backyards when we go on canoe trips in July and August.  It's my experience that people tend to drink more when the water is flavored, be it koolaid, tea or some sports drink mix.  That's the greatest benefit.

Swim/wet your clothes before and after a portage if at all possible.  If you're wet footing the landings anyway, just take a dip on each end.  At the terminus of many longer portages, I walk in to shoulder level if possible and just flip the canoe over.