For auto parts hobbyist / enthusiasts: what car part would you recommend a fellow hobbyist should buy?

What one car part would you recommend another car part hobbyist should buy and why?|||Horns of different sounds.Every time you switch, the car sounds different.|||Intake and exhaust - makes your car sounds great|||I'd put many stick on flame and lightning bolt decals. Those always make the car look faster. And a fake hood scoop and fake fender ports too. Don't forget the fuzzy dice for the mirror.|||Stick-on hula girl for the dash.....