The following works on the mission entitled "Hunted". After fighting your way through a basement (after going underneath a bridge, across a field, et cetera), you'll reemerge outside. A nearby house next to a vending machine and a car should be your target from here. Inside the house, there's a laptop on the table. This is a piece of Intel, and collecting all thirty of them in the game will unlock all of the Cheat options available. If you collect the Laptop, and then head through the nearby checkpoint, it will be permanently acquired on your save file. Kill yourself at this point (a Grenade is an easy way to do so), and backtrack to the house. Collect the Laptop again, go to the checkpoint, kill yourself, and repeat the process. By doing this, you can collect thirty laptops without actually collecting all thirty of them.