Invincibility
During play, press Y, A, X, B, Black.

All Planes:
During play, press Y, X, B, Y, Black.

Ultra Hard Difficulty:
During play, press X, B, A, X, Black.

Super Guns:
During play, press B, X, A, B, Black.

10 Tokens:
During play, press X, B, X, B, Black.

$5000:
During play, press A, Y, A, Y, Black.

Arixo Surprise:
Fly west until you reach an outhouse with a landing strip. Land on the runway to get a surprise (new plane).

Thanks to Revolution readers Pappa P., Matt Halloran and Johnny!