Dan - Thanks for posting this, your story totally freaked me. The odds of slipping through a strainer and coming out relatively unscathed are not great, I'm glad you were one of the lucky ones.
As an avid fisherman, I've spent 40 years fishing the west coast rivers and know the dangers. A couple of suggestions to add to the ones already offered by others. I always carry extra clothes in a dry bag because you can become hypothermic very quickly and exercise isn't always an option (you could have been hurt and had to wait for assistance). The clothes don't have to weigh much if you are concerned about weight and I carry one set that can be used by anybody in my group.
The other thing that I would add is that you mentioned you walked to a road that ran along the river. As a novice, I would suggest that you scout the river with a topo map and mark the areas of concern before your drift. Yes it takes a bit of trip planning to do this but if it saves you from another post like this (or worse) then it's time well spent.
Keep the trip reports coming, I always enjoy your posts!