Which Auto Accessories are Really Useful?

Out of the flood of auto accessories coming to our car markets, which really are useful, and which we can do without?
Everybody would agree, that many are just trash that not only has no purpose to serve the auto owner, but can actually interfere with the driver. Take for example all these funny chains, mascots, crystals hanging from the rear view mirror. If anything, they distract the driver, and compromise the road safety.

But, there are car accessories that are designed to enhance driving experience and safety.
For example:
-navigation systems
-portable coolers
-hallogen long-beam lights
-certified bullbars
-alarm systems and more.

Clearly, it is up to the car owner what accessories to buy. But, spending money on useless gadgets will not improve your car's value, nor your pleasure of driving it. If anything, it means wasted money.