Extra money:
Note: This trick requires a cartridge. Enable the following code: GXNXSVSN to allow your ship to be repaired for free. When it gets fully repaired, put the damage back up. Your money will increase each time you do this. When you take the damage off, the money will not go back down.
View credits:
Press Left, Up, B, Left, Up, B at the game over screen after using all continues.