This is way better than airbags, said the crazy person who lives in this car.
Stone Arrowheads: You can pick these up online and with some thread and sticks, make great hunting and defense companions. But a word of caution - be smart about the size of the ones you try and put in your carry-on.
Mini Flashlight: These things are amazingly powerful and have great battery life. Plus, they are super cheap. Tuck two or three away in your carry-on. And throw in a head strap, too.