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 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 its flowing out of solid rock.
Cheats

While playing, pause the game then go to "in-game options/enter cheats" and enter the following codes:
(B), (B), (X), (Y) - Auto Win
(B), (B), (X), (A) - God Mode
(B), (B), (X), (B) - God Mode (Team)
(B), (B), (X), (X) - Refill Ammo