Have Sarge be your co-pilot
On the last mission 16-Plastro's Revenge ,you will be able to play with Sarge by your side as co-pilot. Just look for him in the co-pilot selection screen.

All Co-Pilots
In the passwords screen, type Up, Down, Up, Down, Up, Down, Up, Down.

Fly Super Stallion
Successfully complete Mission 8: Saucer Attack.

Passwords

Mission 2: Going Car-Razy
X, Down, Left (x2), Square, Circle (x2), Right

Mission 3:The Train That Could
Triangle, Up, Left, Right, Down, Triangle, Square, Up

Mission 4: Tan Terror Troy
Down (x2), Square (x2), Left, Right, Circle, X

Mission 5: Bug Bath
Right (x2), X, Circle, Down, Up, Down, Up

Mission 6: Uninvited Guests
Square, Circle, X, Square, Triangle, Left, Up, Right

Mission 7: Ants In the Pants
Square, Circle, X, Square, Triangle, Left, Up, Right

Mission 8: Saucer Attack
Right, Down, Left, Up, Triangle, Down, Up, Down

Mission 9: The Heat Is On
Circle (x2), Right, Up, Right, Up, X (x2)

Mission 10: The Melting Pot
X, Down (x4), X, Left, Right

Mission 11: River Rapids Riot
Triangle, Up, Circle, Down, Square, Left, X, Right

Mission 12: Nightmare Teddy
Up (x2), Triangle (x2), Left (x2), Circle (x2)

Mission 13: Demolition Time
Left, Down, Left, Down, Square, Circle, Square, Circle

Mission 14: Pick Up The Pieces
Left(x2), Up, Right(x2), Up, Down, X

Mission 15: Have an Ice Day
Square, Right, Left, Circle (x2), Up, Down, Square

Multi-Player Passwords

Mission 2: right, up, square, X, up, O, up, right
Mission 3: left, down, left, down, up(x4)
Mission 4: square, X, X, square, O, triangle, triangle, square
Mission 5: O(x2), square, down(x2), square, X(x2)
Mission 6: X, up, O, down, triangle, left, square, right
Mission 7: up, down(x3), right, left(x3)
Mission 8: left(x2), triangle, right(x2), triangle, up(x2)
Mission 9: square(x3), O, down(x3), left
Mission 10:O, up, left, square, up, left, down(x2)
Mission 11: triangle, O, triangle, O, up, up, down, down
Mission 12:up, down, left, right, O, O, up, square
Mission 13:X, left(x3), square, triangle, O, X
Mission 14: left, down, left, down, square, O, square, O
Mission 15:down(x4), X, X, O, O
Mission 16: triangle, down, triangle, down, square, up, square, up

Unlock all helicopters in 2-player mode
To get all of the helicopter in 2 player you must first go two the cheat code menu and enter Down, Down, Down, Down, X, X, O, O

Fly Apache
Successfully complete Mission 14: Pick Up the Pieces.

Fly Chinnok
Successfully complete Mission 4: Tan Terror Troy.