Fighting Force 64
Air Base Gun
When you get to the Air Base go to the left and there should be a A-10 plane. Destroy it and a huge gun will fall out the front. It is very heavy for everyone.
Credit Goes To: Garrett via IGN 64

Secret Weapons in the Lift
Have you ever run out of weapons to use in the Lift? If so my friend and I found a cool trick to get more. With any character go by the side of the lift, where the handle bars are, and simply press "A". If you don't have a weapon at hand your character will instantly pull the handle bar off and use it is the "steel rod" weapon. The best part about this trick is that you can use it for granted, because there are four, two on each side of the lift!
Credit Goes To:W0LfPacWcW@aol.com via N64cc
 Air Base Gun
 Secret Weapons in
 the Lift
 Level Select &
 Invincibility
 Rocket Launcher
 Find Flare Guns
 More Ammo
 Weapons at the Start
 of Stages
 Special Moves
 Big Weapons
 Cheat Menu
Level Select and Invincibility
At the main menu, PRESS and HOLD L + Z + C-Up + C-Down. This will take you to the character select screen in a few seconds. From there you may press C-Left or C-Right to choose your starting level. You will start with invincibiliy.

Rocket Launcher
On the car park stage if you break the police car a rocket launcher will come out the trunk.

Find Flare Guns
On the hovercraft stage there are two black structures on either side. Destroy those and a flare gun will drop out of each structure.

More Ammo
To get a weapon that holds 10 shots instead of 4 or 5 shots in your weapon, do the following. When you are at the character screen, push C-Down, C-Up, L, C-Right, C-Down, and then press R. When you do this code you will hear a voice say "Alright".

Weapons at the Start of Stages
When you about to finsh a stage pick up any weapons from the ground and take them with you to the next stage.

Special Moves
Each character lists a special move at the end of their character bio. Each of these button configurations work for all charcters giving each chracter 4 special moves.

Big Weapons
Car Engine -- If you completely destroy a car(ex. a bazooka shot), you can grab the car's engine. This only works with Smasher.

Airplane Gun -- On the Air Base stage, go inside the hanger and destroy the plane. After it is destroyed you will be able to use its gun.

Cheat Menu
At the main menu, press Up + B + C-Left + C-Down + Z until a gun shot is heard. Now go to the OPTIONS screen to access the cheat menu.