We have a load of steam backups available on site for all of the games that we play at BreachLAN, including updates, patches etc.
Although you can grab this off of the network, sometimes its easier to do with an external (portable) hard drive.
The stuff you really need I've listed below
PC, Monitor and all cables / peripherals that you require (keyboard, mouse, gamepad, mouse mat)
4 way power extension - you get 1 power socket
All your games discs / Windows discs / Anti Virus (for a complete reinstall if things go belly up)
Sleeping bag, pillow, wash bag, change of clothes
Money for food (bring some too, cause its a bit of a drive to the shops)
Hope this helps