The "lightest" way is just to duct tape your rain pants to your boots really tight, and maybe throw a strap at the ankle and wade on through. Actually, I guess the lightest is to strip to skivvies and wade it. But that gets really old when water temps are in the 30s, and especially if you are crossign the stream multiple times. I'd be hesitant to try a garbage bag based on the one experience of taking water over the top of the sourdough slippers.
