Activating this trainer:
If not state otherwise below, press F1 at main menu.
Listen for 'Trainer Activated'.
Press desired hotkey. All hotkeys can be changed on the trainer.

Promo Options:
NumPad2: Unlimited Ammo

Trainer Options:
NumPad1: Unlimited Health
NumPad2: Unlimited Ammo
NumPad3: No Reload
NumPad4: Unlimited Items
NumPad5: Calm Heartbeat
NumPad6: Unlimited Sniper Focus
NumPad7: Super Weapon Accuracy
NumPad8: Sniper Stealth Mode

Notes:

Unlimited Health:
Toggle on to try and keep health full.  This will protect you from most gunfire, but not severe damage or explosions.

Unlimited Ammo:
Toggle on and most weapons will not lose ammo when you reload.

No Reload:
Toggle on and most weapons never need reload.

Unlimited Items:
Toggle on and many items in the game, you have unlimited amounts of them, such as grenades, mines, explosives, etc.

Calm Heartbeat:
Toggle on and your heartbeat remains calm.

Unlimited Sniper Focus:
Toggle on and when you engage the focus while sniping, it remains low.

Super Weapon Accuracy:
Toggle on and many weapons have extreme accuracy.

Sniper Stealth Mode:
Use as directed!  This will make you invisible or less detected if you have it on BEFORE you engage enemies or BEFORE they see you.  Once you have been seen, they can continue to attack.  Also, this may disable certain actions while it is on, so if you cannot use a device, engage something you can interact with normally, or cannot place an item or explosive, make sure enemies around you are dead or do not see you, then toggle back off to allow the action.