I believe the kubotan is illegal in some countries - UK in particular.
A cane/walking stick is a nice improvised weapon, especially if you have a legitimate reason to carry one in public. A concealed sword/dagger inside the cane, well, that's another story....

Other improvised weaponry - crutch, umbrealla, leather jacket, belts, handbags, short piece of cord, piano/guitar wire, guitar (although I wouldn't be using a Washburn or Fender for that purpose), bike chain, bike helmet, bike tyre, bunch of roses, feather duster (although why you'd be caught dead walking down the street with one is beyond my imagination).... lots of seemingly innocuous things can be used as weapons - limited by your imagination....