Infinite ammunition
To get unlimited ammunition, enable the "All weapons" code continuously until whatever you want is at 9999 shots. The next time your clip runs out, it will reload automatically but the magazine (9999) will stay the same.

Infinite Flamethrowers
Put out twenty fires on each of the three islands (about sixty total) to get unlimited Flamethrowers at your hideout. Note: This does not have to be done all at once.

Infinite Health icons
Save fifty people on paramedic missions to get unlimited health icons at your hideout. Note: This does not have to be done all at once.

Infinite Adrenaline Pills
Save fifty people on paramedic missions to get unlimited Adrenaline Pills at your hideout. Note: This does not have to be done all at once.

Police bribe
Get 45 kills in vigilante mode to unlock a police bribe that is available at your hideout.

Faster taxis
Get 100 fares in cab mode to unlock faster taxis available at Borgnine in Harwood in Portland.

Bonus Buggy
Successfully complete the Mafia missions in story mode to unlock the Buggy. Return to Portland and go to the Diablo parking lot (where the mission phone is located) between 19:00 to 24:00 to find the same Buggy glimpsed in Joey's garage from the Mafia mission. It will appear in the same location and change color each time.

Easy "infinite" run
To continue to run at a fast pace without fatigue, just tap X instead of holding it down. This helps when trying to give your character "exercise" so that he can run for longer periods of time as well.

Stealing police cars
To easily steal police cars, press Triangle at the drivers' side door. Then, as the policeman gets out, go to the passenger side and get in.

Use cars as a bomb
If you need a big bomb and you do not have the money for Eightball, smash your car into things and use it as a bomb on wheels when it starts to burn -- but make sure you get out of the car before it explodes.

Getting guns
Go by Toni's place to find an alleyway where an Uzi is located. Go near the mob car on the ledge in the other nearby alley -- you can go between two buildings and find an AK47-like rifle and some armor.

Hidden packages
When you see the Rockstar billboard, there are usually some items nearby. On the three islands, hidden packages are usually found near the billboards. For every ten hidden packages you find, you gain access to a new weapon located at your hideout, free of charge.

Programmer message
Go to the parking lot where you had to take out the men with bombs on their chests. Use the Dodo or a pile of cars to get on the other side of the wall that surrounds the area. Once in there, look for a poster with a secret message.

Regain health
Car jack any vehicle and drive up to a prostitute walking the streets. Stop and let her approach the car, after a few seconds of talking, she will get in. Drive to a remote area where there are not any cops around (a good place is in your hideout). Stop the car, but do not get out. After about two seconds, the car will start rocking back and forth. You will recover approximately 40 to 50 points of health. When it is over, she will exit the car and walk away, but not before she charges you a fee. At this point you can beat her up and take back the money you just paid her. Note: The prostitute will fight back when you try to take your money back. If for any reason you both have to exit the car before it starts rocking, you will still be charged a fee (beat her up to take it back). You cannot do this with the same prostitute twice in one night -- you can however, pick up another prostitute and recover more health. Even though the maximum amount of health points is 100 when you start the game, it increases to 125 after the encounter and remains that way.

Get to Shore Side Vale early
Use the following trick to get to Staunton Island before the bridge is fixed and before the subway is open. Go to the bridge to Staunton Island. Go past where the blockage cones are located, to basically be on the bridge. Enable the "Dodo car" code (press Right, R2, Circle, R1, L2, Down, L1, R1), then the "Tank" code (press Circle(6), R1, L2, L1, Triangle, Circle, Triangle). Make sure you are all the way back to get enough room to take off using the tank (as a plane). Start firing the cannon backwards and accelerate. Keep firing the cannon backwards, and just as you get to the edge where the bridge has been broken, you will take off. Try and get back on the ground. If done correctly, you will now be on Staunton Island and when you cross the bridge, the "Welcome To Staunton Island" screen will appear. Then after you get there then go to either the porter tunnel or the subway. If you go to the subway, take a yardie lobo in there. Then get out of it, once you get all the way in the subway. Then go and wait for the subway car to get to the station, get in it, and there you go. Now stay in the car until you see in the lower right hand corner of the screen, a message that says: Francis Intl. Airport. and guess what? You are now at the third level, with out doing any missions.Note: You can use nearly any car, but the tank has a better ability to fly higher. Also the game gets confused and the cartel still shoots at you.

Flying Dodo car
Take the Dodo to the very end of the runway. Turn it around so its facing away from the edge. Hold X to build up momentum, while holding Up. Once you get enough speed, quickly hold Down. Once airborne, use normal controls to level out the car. Note: The small wings make extended flight extremely difficult, if not impossible.

Fast tank
To get the tank to go extremely fast, turn your turret to face directly back, then fire repeatedly. Watch your shots -- if you hit any cars the cops will chase you. This is especially useful for the Vigilante missions.

Flying tank
Get the tank, then turn the turret backwards and find a long road. Start shooting it as fast as you can to speed up the tank, hold Left Analog-stick Down. If done correctly, the tank will become airborne allowing you to actually fly it around.

Tank storage
The game will remember the location of tanks, no matter where they are. Enable the "Tank" code (press Circle(6), R1, L2, L1, Triangle, Circle, Triangle), then park the it near your safe house. Save your game, and when you load it again the tank will be where you saved it. Note: It is not necessary to ever park it in the garage.

Free repairs
Park your car(s) in the garage at the save point. Exit, then go in to save. You can either save your game or cancel. Either way, your car(s) will be repaired.

Free paint jobs
Go to pay and spray once. Pay the $1,000 for the new engine and paint job. Then, immediately drive back in an get a new paint job, free of charge. This can be done as many times as needed until you get the desired paint job.

Drive-by shooting
Get the Uzi and enter any car. Press R2 + Circle or L2 + Circle and your character will shoot the Uzi out either side of the car.
Secret race-type mission in Staunton Island
In Staunton Island, go to the Super Saver Grocery Store in Newport. Enter the car in the parking lot to get a secret race-type mission, where you must go through check points.

Yardie Lobo car in Staunton Island
In Staunton Island, drive around your garage (around the block or elsewhere), and find a red car with a white top and panther colored seats. This is a gang car, called the Yardie Lobo. Once you find it, press R3 and move the Analog-stick Up, Down, Left, Right, or diagonally to move it. Press L3 to make the car push up and remain that way. Press the L3 continuously to jump with your hydraulics.

Hidden package in Staunton Island
In Staunton Island, there is a hidden package on the hospital roof in Stauton Island. The package is on the corner of the building directly across from the stairs. To get the package, park an ambulance parallel, right next to the building where the package is located. Then, park any "van" perpendicular to the ambulance. Then, park any "car" next to the van. Finally, just jump onto each vehicle to get to the roof. The hospital parking lot contains plenty of vehicles to choose from.

Fastest car in Portland
In Portland, go to the Capital Auto shop. Take a big car and ram it into the glass on the store to break it. Inside is the fastest car in the game, which resembles a Shelby.

Mini-game in Portland
In Portland, near Toni's place, is an alley with a parked van marked "Toyz". Get in the van to play a rampage mini-game involving an RC car with a bomb attached to it. You get $1000 for each Mafia car you destroy. This game can be played as many times as desired.

Flamethrower in Portland
In Portland, get a decent car, such as the cab or something that is not too heavy. Drive from your hideout in Portland to the end of the road to your left. Turn around, and drive on the grass under the monorail tracks. On the left section of grass will be a jump made out of concrete. Jump off it, and try to land on the monorail tracks, or at least on the stairway so you are facing the same way that you were driving. Drive in-between the tracks, as you do not want to take a chance at getting knocked off by the monorail. You will soon see a glowing circle on your right, which is the flamethrower. Drive over to it, and park next to the ledge-type object below it. Jump onto the hood of the car and take the flamethrower. Save the game at this point, as it may be difficult to get it again.

Molotov cocktails in Portland
In Portland, go to 8-Ball's auto yard, and take the path leading to the garage. Before you enter the garage is a path leading left. Take this path, then go straight until you find train tracks. Turn right following, the train tracks. This leads into a tunnel. Keep going until you find a group of bums. Run over and kill them. They will leave Molotov cocktails and a hidden package.

Drive on elevated train tracks in Portland
In Portland, in the highest area of Portland is elevated train station. The path leading up to the tracks is large enough to fit a car.

Avoid police chases
After stealing police cars, you are relentlessly pursued by the police until you are captured or injured. In order to avoid this, steal the police car (try smashing them until they get out to arrest you, and then jump in their car). Take the stolen police car to your garage (the condition does not matter), and save the game. When you return with the stolen police car later (from your garage), it will be viewed as a normal car by the police, but will still be able to do the Vigilante mission.
First, find badges. The best places to look are in the alleys and parking lots. If being chased in a car, and you are not about to explode, just keep running, and try to not kill anyone. Sometimes, if you drive around enough in harsh conditions, the cops will just stop chasing you. This only happens if you have one or two stars though. If you have around four or more stars, quickly find some badges. The cops are reckless around them, and will do anything to get you busted, or most likely killed, even if it means accidentally killing a few witnesses.

Items
The following items are always available at your safe house, and regenerate. The numbers indicated the number of hidden packages needed for that item:
10: Pistol
20: Uzi
30: Grenades
40: Shotgun
50: Armor
60: Molotov cocktail
70: AK47
80: Sniper Rifle
90: M16 or Flamethrower
100: Rocket Launcher