"I also had to improvise a "web sling" that I'm back home now and perfecting. Everytime I've hoisted a dry bag of food I've prayed silently that the backpack straps wouldn't tear out of the bag!"

I just keep one extra piece of rope in my kit - just 1/8' paracord type of stuff, maybe 15' long?  I just wrap that around the food bag (vertically) maybe 3 or 4 times, and clip to that, not to the shoulder straps or grab loop.