Cheat mode:  Go to the options menu and choose "Cheats". Answer the series of seven questions with the following to unlock the entire game.

1. Squid
2. Conroy
3. Tito Makani
4. Maurice
5. Ocean Shores
6. Otto
7. Eddie:Prince of the Netherworld

Extras  -  Get a score of 750 on the shooting gallery to get The Brains that Ate California for 2 Gold Coins and 2 episodes of Rocket Power

Be Pi Character
Get 20 Gold Coins
Be Sputz Character
Get 30 Gold Coins
Be Lars Character
Get 40 Gold Coins
Be Eric Golem Jr Character
Get 50 Gold Coins
Be Eddie Character
Get 60 Gold Coins

Gameshark codes

Enable Code (Must Be On) 92CDF654 B063  8D817C91 8374  C9BED072 439D
Infinite Health 00996502 924B
Infinite Yellow Rockets E70F3F54 62A8
Infinite Red Rockets 6F570AE1 4286
Infinite Pucks E70D3F54 E2A8
Have All Arcade Prizes [Note 1] CCB2BE97 344E  95E68F1C 6930
Have Oil Squirter 48FAC483 1247