When Mission 3: Glassed begins, proceed forward. After passing the first structure on the right, you will see another building with a set of stairs. Go past the stairs and underneath the building. There is a room you can enter on the left that contains a Blu Soda vending machine. Go up to it (works best while holding the assault rifle) and "Activate" will appear. Activate it three times to spawn a magnum, activate it three more times for a shotgun, and activate it three more times to get the SAW. The SAW weapon is especially useful when playing the mission on the Heroic and Legendary difficulties.