Here is a handy tool that makes your air travel experience less miserable. The Soarigami airplane armrest extender/divider keeps you from having to fight for armrests. It clamps onto an existing armrest and provide you and the person next to you with your own space.
The device is fully adjustable and works on armrests from 1.5 inches to 2.75 inches in width. Costs $25 at this time.