During gameplay hold L2 + R1 then press triangle, circle, triangle, circle, square, square, square, X.
All Guns
During gameplay hold L2 + R1 then press square, triangle, square, X, square, circle, square, square.
Easy through greenhouse
When you are going through the greenhouse with the third kid, pots will shake violently, hover and then fly towards you. You can shoot them but that is the hard way to do it. The easiest way is to press L1 to duck right before it hits you. I found this method the easiest.
Full health
During gameplay hold L2 + R1 then press X, X, X, triangle.
Refill ammo
During gameplay hold L2 + R1 then press triangle, triangle, X, X.