Here are a number of improvised self-defense tools:

- a role of coins in a (nylon) sock - assemble only at destination
- a sturdy steel pen (Lamy, Rotring, Parker) does the same as a tactical pen but won't get you in legal trouble
- a firmly rolled up newspaper
- a set of keys

The advantage is that these items are allowed anywhere. Only the sock with coins would be regarded as a weapon but in the continuum of violence and escalation used in most civilized countries it would be OK to use that as a WOMAN DEFENSIVELY on a MALE attacker because the male would be normally perceived as having an advantage and this weapon levels the playing field.

All of them can be transported even in your purse or jacket and are per se legal everywhere including on a plane.

Moreover, except the coins in sock and the pen administered brutally at the right spots, none of these things are lethal. So should you lose the "weapon" to the attacker it cannot be used against you with great harm.

Till