Well, my brother (an even bigger sportsman than me!) carries his 'waterpolo cap number number' (for god luck) on his neck/keys layyard in the form of a miniture snooker-ball keyring (a number 5, BTW!). I just notice that this fairly heavy keyring is a deadly missile! In addition to a bunch of sharp keys on the end, I'm sure that this could be a very effevtive weopon.

problem - you need space to swing the 'mace'

with the baton, I can also stab/poke, as part of it is rigid. But to be honest, I think that it is more of a detterent than an actual weapon. If a criminal wants something from you enough to challange you when you show him a weopon, chances are that he will probably get it from you, or at least hurt you trying.