Don't overlook the value of improvised self defense weapons especially something like a pen. I have a purpose made machined aluminum pen that had a pointed end and a blunt impact end. It would be highly effective in targeting just about anything, but especially eyes, throat, groin. These cost about $80-to over $100 retail...luckily, I won mine at a shooting school last month! It has been my flying companion on a couple trips since.
You don't need an expensive pen though, just a sturdy one that fills your hand and can stand up to some abuse. A Sharpie will work. Cold Steel makes a "Sharkie" pen that is cheap. You can look for metal "drug rep" pens on ebay. These are large, sturdy pens made by pharmaceutical companies for advertising...it may have a herpes medication written on it...but they work!
If you have to use it to protect yourself, just grip it tightly in your fist and target whatever vulnerable anatomy is available. A sturdy pen will help you fracture ribs...a standard pen is best targeted at soft parts or it will break (expect it to break after a strike or 2 anyway).