I'd be curious to see how much those in the know here could add to a list of video game references:
Doom:
Almost too many to list
Eric's "straight out of Doom" pump-action shotgun
Named it Arlene from the Doom novels
References an AB-10 from the Doom novels several times, got Dylan a TEC-9
Dylan has the double-barreled "super shotgun" from Doom II
sawed off their shotguns
The carbine rifle taking the same 9mm ammunition as the TEC-9, resembling former humans gun which has the same ammo as the chain gun. Also Doomguy seen in third person carries some kind of long gun
Eric's wooden berserk
The white and black shirts resemble former humans tan shirt and shotgun guys black shirt.
The ammo pouches and even the vision of exploding buildings resemble the Ultimate Doom cut-scene.
Eric says he was always at the bottom of "the food chain", which probably comes from the Playstation Doom poster:
[You must be registered and logged in to see this link.]Calling themselves "indigo" and "green" probably came from the color of their Doom characters when playing multiplayer.
Duke Nukem 3D:
Pipe bombs
bandolier
talk of ripping heads off
In both Doom and Duke Nukem 3D, if you shoot (or in Duke Nukem, also toss a pipe bomb) at a barrel or canister it explodes taking out possibly several enemies. Eric shot at the bombs thinking they would explode, and tossed bombs into the cafeteria earlier perhaps for the same reason, as well as Dylan's tossing a molotov at it. This is sometimes described as a "chain reaction" which is how Eric described his 'revolution' and copycats.
In both you can switch between a shotgun for stopping power and a chain gun for speed, and both E & D carried both a shotgun and something which shot faster at the same time.
In both you have a rocket launcher/RPG which kills you quickly if you shoot it too close. May have been the initial reason for trying to make napalm, and it being the 'suicide plan'
Wolfenstein 3D:
I suspect where Eric got his first exposure to German and the Nazis being cool.
Postal:
Eric shot himself in the mouth, as Postal guy does after saying "I regret nothing".