I'm so sick of saying this, but only Game Freak knows this for sure. We do not have full confirmation of what they are at this point in time. I'll try to answer this anyway:
- Bulbapedia's page on Lysandre says that the robotic machines on his back were supposed to power the ultimate weapon.
>Lysandre's cybernetic suit, the Lysandre Machine, was meant to be used to drain Xerneas's/Yveltal's power into the ultimate weapon.
- The visor matches with the ones that the Team Flare Admins and Grunts wear. They're basically the same but in different styles and colours. From what I can tell they're just there to look good, they don't have any real purpose.
- Can't find anything about the gold object on his arm. Perhaps it's just another part of his suit?