During a mission press start to pause the game, choose In-Game options, choose Enter Cheats, then enter one or more of the following button combinations:
Code - Effect
B, B, X, Y - Complete Current Mission
B, B, X, B - Team Superman (Team Invinvibility)
B, B, X, X - Refill Ammo
B, B, X, A - Superman (Player Invincibility)
Under Armor reference
During the training mission, go to the rifle range and get a sniper. Stand in front of Alicia Diaz. Make sure you are standing on the range and she has her weapon down. Zoom in on her neck. Notice that she is wearing Under Armor, and that it has the Under Armor logo and writing on it.
Water source
In all the levels with a river or stream, if you follow it to its source you can see that it's flowing out of solid rock.