Extra Money:
As you arrive in Apple market you'll see two trash cans and a couple of boxes. Kick the can behind the counter of the backey in which you will recieve 1000 zenny. Also look inside the trash cans and you will get 50 and 100 zenny and look in the boxes in which you will recieve the same amount of money as when you looked inside the trash cans for 50 and 100 zenny.

Hard Difficulty:
Beat the game to unlock the hard difficulty setting.

Easy Difficulty:
Beat the game under the hard difficulty setting to unlock the easy difficulty setting.

Start With Jet Skates and Buster Max:
Beat the game under the hard difficulty setting in less than 8 hours. The Jet Skates and Buster Max will already be available at the start of the next new game.

Get a Laser Arm:
Once you join the gang and they finish building the "base", you get X Buster. Then, go digging until you have the second laser part (you can find out if it's a laser part by pressing start and selecting Normal Item and reading the explanation at the bottom). Then, beat all the obstacle courses at the KTOX Tv Station. Then go to the museum and talk to the girl at the top of the stairs. She gives you a Prism Laser. Go to Roll and Item Development. She'll give you the Laser Arm!

Thanks to Revolution readers Johnny Volop and James Hillert!