Which Rocket League Items Can Be Shared Across Linked Accounts?

Each platform you link to your Epic Games Account shares its inventory with the other connected platforms, with a few exceptions.

Shared

All earned free drops (Common Items, Event Items)
Season Rewards & Titles
Rocket Pass Items
Item Shop Purchases
- If an Item Bundle includes Credits, those credits are only available on the platform where the bundle was purchased. The items will be shareable across other platforms.
Blueprints and items built from Blueprints
All Rocket League-branded DLC from the Legacy Pack
Esports Shop Purchases
Fan Rewards
RLCS Attendee items
Premium DLC (Back To The Future, Jurassic World, DC Superheroes, Fast and the Furious, Ghostbusters, Knight Rider, etc.)

Platform-Exclusive Items: (Sweet Tooth, Hogsticker, Armadillo, Mario and Luigi NSR, and Samus' Gunship)
Premium DLC purchased on Nintendo Switch
Ultimate Edition On-Disc DLC: Batman/DC Superheroes Pack
Purchased Credits balances