Windshield so you can see where you're going.

Brakes so you can stop the thing.

Steering column and driver's seat to help you maintain control of the vehicle.

Alignment to keep it from eating tires.

The other stuff is more "nice to have" than "actually important".

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.