Easy money:
Go to Apple Market and kick the can into the bakery. The woman behind the counter will give you 1000 Zenny. Enter any shop and exit. The can will reappear. Repeat this as many times as needed. Note: This will still work when everyone leaves.

Go to the market just before the main city (the junk store is found here). At the south entrance/exit, you can find a small yellow can on the ground next to a garbage pail. Start kicking it until you put it behind the counter of the larger of the two bread stores. A "Nice shot! Bonus 1000 Zenny" message will appear, followed by Remember to recycle your empty cans". You can exit and re-enter the market and repeat this as many times as needed.

Play the beast hunter game at the Studio to get 4000 Zenny for completing grade A. Repeat this as many times as needed.

Once you have destroyed the Bruno robot in Old City, go in the gate down to the Main Gate. Destroy the fire breathing dog. Collect the Zenny with the Vacuum Arm. Exit where you entered, and repeat as many times as needed. Before that though, there are "beehives" in the Cordon Ruins, where you get the Yellow Refractor. As long as you do not destroy the "hives" themselves, they unleash a unlimited number of flying enemies.

Use a high powered gun such as the Shinning Laser in places like the Underground City, Uptown, and Downtown to get more money than with the Buster Gun.

Hard difficulty:
Successfully complete the game to unlock the hard difficulty setting.

Easy difficulty:
Successfully complete the game under the hard difficulty setting to unlock the easy difficulty setting. Alternately, successfully complete the game with a time less than 3 hours. Note: The Bust Max will be available at the start of a game in easy mode.

Start with Jet Skates and Buster Max:
Successfully complete the game under the hard difficulty setting with a time less than 8 hours. The Jet Skates and Buster Max will already be available at the start of the next new game.

Hitch a ride:
Sometimes you can hop on the cars that go through the town and go anywhere it takes you. This is very easy with a truck because you can jump on the back and hold on.

Get the key quicker:
When you go off to fight Servbots in the yellow, red and blue robots, go to the blue one. Get right next to it and throw the mines at it. After a few hits, it will explode. The key will be floating up in the air.

Skip streets:
Acquiring the Jump Springs allows you do more than hitch rides around town. You can leap and catch ledges of buildings -- allowing you to completely skip some streets.

Finding items in trash cans:
If the lid flies up on a trash can when you kick it, nothing is in it. If the lid stays, there is something in it.

Exploding items:
Trash Cans, Soda Machines, and Boxes will explode violently if hit with a explosive or the Drill Arm.

Free soft drinks:
There are two ways to get free soft drinks. If you are inside the Flutter, go to the living room. There is a cooler with unlimited soft drinks in it. If you are in the city, find a vending machine and kick it. A soft drink will come out without you having to pay.

Quick energy cubes:
To quickly gain a little health in battle, shoot a Servbot until he is smoking, then kick him a couple of times. At least two energy cubes should appear from each Servbot.

Black armor:
Destroying public property, the News Blimp (when Bon Bonne is attacking City Hall) or keeping the stolen bank money will turn your armor black. People also will not like you.

Keep on using the "kick the can" easy money trick to turn your armor darker. Eventually it will be black and dark blue. If you can get to this color, you can defeat Bosses much easier, and people will still like you. As a plus, you can also get a lot of money.

Winning the racing mini-game:
Pull back to brake the skates and turn easier, and push forward to speed up.

Opening the museum:
Get the Lipstick from Hipbone after talking to the artist, and take it to her.

Walk through a Reaverbot:
Get every special weapon in the game. When you do this, you will be able to walk through the Reaverbots, but you cannot guard against their weapons.