The above may help with legal considerations.
The grey area is the word "reasonable", but it is important. It means there is no carte blanche to unnecessarily injury someone who has attacked you and they are no longer a threat - ie stamping on their head if they end up on the floor.
What is reasonable for one person to do in a given situation may not be for someone else. For example a woman may have to be more brutal in defending themselves against a large man than if the situation was the other way round.
As for carrying weapons for self defence, it can be dodgy ground. If you've got it, at what point do you deploy it or use it? Do you practice deploying it quickly?
Surely if you can hit someone with a kubotan ("I thought it was a large key ring, officer"

then you can hit them with your mobile or anything to hand or your fist?
I like the hat idea, though it may have a flinch reaction you don't want if you're looking to hit them - ie they raise their hands in front of their face.
Bottom line is that you have to do whatever you have to do to protect yourself. Hence the old saying "better to be judged by twelve than carried by six"
take care
Steve