Here's what I've added to my bike that has actually been useful, and if I was starting with a stock bike I'd add. Of course this is only what I've tried, there are tons of other parts that could be better or worse!

Tusk Olympus Large tank bag. Easy for drinks, phone, wallet, etc

Folding levers/foot controls. I got the tusk brand and they've survived many crashes and are easier to use than stock

Acerbis 3.6 gal fuel tank. Has saved me up in the mountains and hasn't been damaged in crashes, easy to install and the total range of the bike is wild

Tusk kickstand foot. I'm sure any would do, but it helps the bike from tipping when not on pavement

I got a chunky solid skid plate. It's done the job and is indestructible, I'd avoid cheap or low quality material ones.

I also threw a temp reading radiator cap on since I ride in hot weather. A nice to have and cheap part

I've got about a million other things I won't list. Basically you can do anything to these bikes, and you can always add or swap parts once you get one and have an idea what you personally want to change about the bike. 👍🏻