Cheat Mode:
Beat the game and save when asked. Select "Game settings" on the options menu, and enable the cheats. Load or start a new game to begin with 999 ammo, all weapons, and all combos.

Recharge:
After unlocking cheat mode, turn it on. Start a game and press X, X, X, Square, Square, Square instead of using medkits and your energy and turbo bars will refill.

Combos:

The Shocker  Triangle, Triangle, Triangle, Circle, X
Grand Slam   Circle, Ccircle, Circle, X, Square
Spinal Crush Triangle, Circle, X, X, Triangle, Triangle, Circle, Circle
GOTCHA!      Triangle, Ccircle, Circle, X, X, Circle, Square 

Hints

Extra Life:
When you start the game instead of going left, go right. There is a garbage bin, go up to the garbage bin and try to pull it by pressing Down + X or Triangle or anyone of the buttons for that matter. Once you get it out of the way go inside and there is a free life and if you go straight you can push the wall and you're at the door.

Thanks to Revolution readers Talosyn and Will!