What is the PlayStation pre-order accessory?

It is an accessory, so it is cosmetic gear rather than a creature or a currency. It rides along with the PS5 advanced collector's edition pre-order, which means two things decide whether you get it: the platform you buy on and whether you buy before launch. Aniimo takes console pre-orders on Xbox too, and that version of the pack carries its own exclusive accessory instead.

If you were planning to pick your platform later, this is the small thing that pushes the decision earlier. Accessories in this pack are exclusive to it, so there is no listed way to pick one up afterwards by playing.

The wider point is that pre-order bundles and extended editions are how you start with extra items and bonuses at all, and the accessory is one line on that list rather than the whole reason to buy.

What the console pre-order pack costs and contains

The Collector's Edition pre-order pack on console runs $20. For that you get the exclusive in-game accessories and the Collector's Companion Guide, with its handbook rewards attached.

Not settled: Whether the Collector's Edition pack includes a Primegy Battery is not settled. It is listed explicitly on Xbox next to the handbook rewards and the exclusive accessory, but it is missing from the PlayStation descriptions of the same pack.