What content is shared between my platforms in Fortnite?

In Fortnite, all your items are shared between your platforms linked to the same Epic Games account.

Example: If you purchased the "Ghoul Punk" bundle on your PlayStation, its contents will be available for use on all other platforms linked to the same Epic Games account your PlayStation is linked to.

The only exception is V-Bucks bundles. V-Bucks purchased on other platforms are not shared with Nintendo Switch, and vice-versa. For more details regarding this, please check this article: Why don't all of my V-Bucks transfer across platforms?