*Dead Man Walking Level - When you enter the church two guys will corner you dispose of them and head to the back right corner inside. Take off the crooked door with a shotgun blast, enter and blast the left wall twice with the shotgun to reveal a hidden room containing a Purple Rune Stone. Also note outside the church behind the fence is a huge purple rock with the same markings as the rune stones. I as of yet have not found a way back there or discovered the means of the rune stones.
*White Lightin' Level - Make you way through the shacks until you come to a house there will be TNT on the right side of the house, and inside will be a table fashioned out of a door and two barrels. Toss a light TNT stick into the back wall of the house to reveal a hidden room with another Purple Rune Stone.
*Shootout at the Lazy 8 Level - Enter the house from the side door and blast a couple of shoots with the shotgun at the middle of the wall as you walk in to reveal a hidden room with yet another Purple Ruin Stone.
In order to start with more ammo, select "New Game" at the main menu, while holding the L and R triggers.