Brian, have you ever tried bread bags as less of a vapor barrier and more of a liquid barrier for wet weather/standing water? The reason I ask is that, when I tried, they developed holes very quickly and failed to keep my feet dry. I want to try roasting bags next.
For hiking, I've never found any plastic bag that worked for any length of time - they all developed holes, including roasting bags. Of course, I only care about dry feet when hiking when it's cold - otherwise I just hike in wet feet (I'm lucky, I can walk all day in wet feet and it doesn't bother me, as long as I dry them at camp and keep them dry overnight).
For hiking in cold, wet weather, I use Rocky Goretex socks. They're the bomb. But you need to size up, and they're rather difficult to put on/take off since they don't stretch.