"Needs" nothing out of the box. But, some possibilities might be-
Springs for tuning - Comes with gold/gold F/R. Orange/Yellow nice to have up front, maybe red/white for the rear.
Alumium servo horn? Unless you are a plastic/'saver' kind of guy.
As far as 'bling' goes - already has the gunmetal hexes, shock caps, hinge pin mounts,etc. As it should for a >$500 kit.
Aluminum battery posts with the thumbscrews are a nice addition. Comes with two sets, so if running shorty will have a spare, or set to sell to another zx6 owner.