When you have enough money to buy armor, spend it on them. It will be as if you have double health.
Successfully complete the game and get all the FlashRAMs. Go to the police station. Go to the Hackers screen and "Unlock Cheat Suit" will appear. Go to that and do the phases. After all three are completed, go to the tailors. The Cheat Suit will be available for $100,000. You can buy and upgrade the suit to get better cheats.