Before you use the custom parts on the VP70(Handgun), Desert Eagle(Magnum) or Shotgun use the remaing ammo in the clip/breech. When you use the custom parts to upgrade the gun it will automatically be fully loaded. This may seem like a small amount of ammo but can go a long way in the harder difficuties were ammo is rarer.
Get new costumes
Start an A Scenario with either Leon or Claire. Start the game, but DON'T COLLECT A SINGLE ITEM. Don't collect the weapon in the Gun Shop, any ammo. Go to the Police Station and down the stairs in the courtyard. A zombified Brad will be there. Kill him one way or another (by collect ammo in the RPD or stabbing him). Collect his ''Special Key'' and take it to the RPD Darkroom. Open the locked by the door and you get new costumes!
Secret Film (Film D)
Go to the S.T.A.R.S. Office with Leon or Claire. Search the Desk that says ''It's trashed. Someone must have searched the desk''. Search it 50 times! You'll get Secret Film D.