Instructions
Enter into Level 14 of "Halo Wars" while in "Campaign" mode.
Kill 20 vampires while in the level to accomplish the objective. On the map in the top right corner, the location of a skull will flash briefly.
Travel to the second "Covenant" base on the map and look behind the base for the skull. Once you have collected it, you will now have access to the "Bountiful Harvest" cheat, which increases your supplies by 25 percent each time you use it.
Click the "Start" button on the Xbox 360 controller to pause the game and select the "Skulls" option. Select to use the "Bountiful Harvest" cheat to increase your current supplies by 25 percent. Continue using the cheat to acquire as many supplies as you desire.