How to access the extra cars:
Beat Galaga '88 by getting a Perfect score of 40
Go to the Select option and you can pick your cars

How to access the secret cars:
Take first in each track (novice, advanced, expert) then go back and race
each track in Time Trial mode. After beating a track you will then have 
access to the special car for that track. The 3 cars are: Devil #13, Kid Car 
#13 and White Angel #0

How to access the secret bonus
Do not shoot any of the ships in the game Galaga '88. After all the ships 
have gone by, the game will display a small firework burst and say you have 
accessed the secret bonus. Go to the Other screen and you will now have 
access to set the game setting, from Normal, Morning, Evening and Night.

To access the secret 4WD game in RRR you must first get a perfect score and 
100% hit rate in the Glaxian game at the start. To do this all you need to do is Hold 
DOWN, L1, R2, TRIANGLE and SELECT whilst the game is booting up. Keep holding 
them for the entire Glaxian game and Bingo you will get 100% in the game. When 
you start any race or TT you will have a very funny looking 4WD vehicle.