Have All Guns
To have all guns, press Y, A, A, Y, X, B, B, X, A, X, B, Y.
Press Up, Down, Up, Down, Y, A, A, A, X, B, B, X.
First pause game, then go to map option and put in Y, X, X, B, Y, X, X, B.
Press Y, B, A, X, X, A, B, Y.
If a gang of cops or rival gangs are coming after you, learn to drive and shoot in reverse. Back away from the cars that are about to explode or the explosion will take off a tremendous amount of armor.
Listen for the weather report on the radio. When you hear the report for the tornado warning, find the tornado and follow it from about a block back. You can pick up all the scavenger parts from the vehicles that the tornado destroys. For extra cash, try to induce a RIOT near the tornado. The increased traffic and constant stream of cops will give the tornado more toys to toss around and give you more cash.
Weapon power-ups respawn immediately
Press Start to pause game play and highlight the 'Map' option. Then, press Y, A(2), Y, X, B(2), X, A, X, B, Y. The sound of an engine will confirm correct code entry. You still need to find where the original weapon power-up appears, then collect it again. It will also cause some weapons which you have not unlocked to appear next to your garage. However, not all weapon power-ups are next to your garage. They are usually nearby, but on a ledge or around the block.
Exit the RIOT mode
If you are getting beat up by the swarm of cops that come out in full RIOT, go to the garage and park. The RIOT will be turned off. To save your progress, you will have to pull into the garage again.
When you progress enough, you will be taken to another city by following the 'M' on the map. You can actually go back to the previous city at anytime. Pay attention where the exits are for the cities.
Stay by your garage and induce a RIOT by killing the civilians and other gangs on the street. To get the RIOT factor up faster, blast away the street cops. When your armor is running low, drop by the garage and pick up a repair kit. Keep repeating this until you get enough money for the upgrades. If you 'fail' the RIOT, do not restart by loading the previous save. This allows you keep all the money, no game penalties will be levied, and you will keep all of your upgrades. The only thing you will lose are all of your weapons.