There are various rewards featured in Pit Pass you can claim when reaching and unlocking milestones. There include:
Currency
Car Components
Drivers
Boosts
Official Team Liveries
Crates
Asset Bundles - these are Crates filled with assets only, these contain assets from within a Series range. For example, a Series 1-5 Asset Bundle will contain assets anywhere between Series 1 to Series 5, whereas a Series 3-5 Asset Bundle will contain Series 3 to Series 5 assets.
Currency
Car Components
Drivers
Boosts
Official Team Liveries
Crates
Asset Bundles - these are Crates filled with assets only, these contain assets from within a Series range. For example, a Series 1-5 Asset Bundle will contain assets anywhere between Series 1 to Series 5, whereas a Series 3-5 Asset Bundle will contain Series 3 to Series 5 assets.