What mods do you need for the RC 390 GP?

The KTM RC 390 GP comes quite well equipped from the factory, but many enthusiasts can’t help themselves and want to make it their own. The world of RC 390 GP modifications, from the simple bolt-on parts to the more complex performance tweaks, is what this question explores. Which upgrades are the most popular amongst owners? Are there certain modifications that greatly enhance the bike’s performance comfort? We will talk about the ups and downs of various mods with regard to cost, difficulty of installation, and effect on warranty. For new owners looking to add to their riding experience and those thinking about buying an RC 390 GP and wanting to factor the possible upgrades into their budget, this is relevant information.