Right after 9/11, there was someone here on FR who suggested using a sock and a bag of quarters as a weapon when flying.
It would be extremely effective, but only for one or two hits, unless you could reinforce the sock with duct tape or something. They will just bust open after a good crack.
The one I made wasn’t using quarters, but some “Now & Later” hard candies. It was my last resort to handle a bully twice my size back in summer camp. Worked like a charm... a couple whacks and he was balled up crying in front of the whole cabin.
Then, before the counselor came, I switched out the candies for another sock and tied it back up. So, when he ratted me out that I used a weapon, I showed it to the counselor, who revealed to the whole cabin it was just a pair of socks, which embarassed him even more. He never gave me any trouble after that incident!