Act assured: You know where you're going, you know what you're going top do, and you will be going to get it done.

Don't keep anything in your hands if you can avoid it. Be aware of your surroundings; look both ways when you get off a bus, out of a car, leave a building.

At night, a small metal flashlight (torch) shouldn't be any problem to carry: use it to "light your path" and if someone comes up to you you can flick the light beam across their eyes, disconcerting them, effectively ruining their night vision, and VERY temporarily blinding them...giving you time to leave the area. Of course, you leave the area immediately!

Screaming is also a good idea.

Locking car doors is a very good idea -- at least in the US, cars rarely burst into flames or explode when they hit something or fall off a cliff (unless you live in Hollywood). Unless there's a spark of some kind, gas (petrol) doesn't ignite even if it leaks from a cracked tank. And locking the doors can prevent you from being thrown out of a car during an accident.