Is there a word to describe a person who always buys what's new?

I mean, is there a word that describes a person who follows the latest stuff? For example, someone who waits desperately for iPhone 6 to come out so he can be the first person who has it among his friends. So he can show off and feel like he is the coolest person in the world.

Solution 1:

A person who is quick to follow latest trends is, well, trendy

A person who is very fashionable or up to date:

Taiwan’s well-heeled young trendies

Although this doesn't quite capture that he does it to "show off and feel like he is the coolest person in the world."

For that, try

swanky

fashionable and expensive in a way that is intended to impress people

a swanky new hotel

PS - note that swanky is approving. You sound like you need a word that's disapproving.

Solution 2:

This would be an "early adopter".

In the diffusion of innovation theory, the minority group (comprising about 14 percent) of population which, after innovators, is first to try new ideas, processes, goods and services. Early adopters generally rely on their on intuition and vision, choose carefully, and have above-average education level. For any new product to be successful, it must attract innovators and early adopters, so that its acceptance or 'diffusion' moves on to early majority, late majority, and then on to laggards.

Read more: http://www.businessdictionary.com/definition/early-adopters.html