I'm absolutely appalled no one has listed a kayak paddle, less than 2 pounds. You could go extreme and get a couple of good oars at 2 pounds each.
The oars I have used could either fix or finish off a bad back. It wasn't from carrying them either.
It helped me but that does not mean it would work for everyone. I got so much better that I use a British Seagull ultralight 40 now. It isn't that light and it is not for sale anyway. I do wish it had reverse though.