As mentioned earlier, the real key to success is organization. If I’m hosting a LAN party with more than four people total, I write up an invitation that lists the time, date, address, and most importantly, everything they need to bring. There are a lot of things that each guest is responsible for bringing.
PC Tower: Each gamer needs to bring their own PC. BYOPC - Bring your own PC is what you can put on the invitation. Each PC should be in good working condition with the games already installed and tested.
Monitor: Now, I usually try to provide as many monitors as I can. Cheap, old CRT monitors work best for this, and like many of you, I have a ton of them just sitting down in the basement collecting dust. Bring those up and put them to good use. But, in the end, the best way to make sure that everyone has a screen is to have them bring it themselves. For many, that’s not a big deal because flat screen LCDs are so much easier to transport than their predecessors.
Ethernet Cable: I have a bunch of ethernet cables, because for small LAN parties, I used to provide them. No big deal. However, if you have a larger LAN party, you should have everyone bring an ethernet cable. On the invitation, say something like, “If this is an issue for anyone, give me a call.” Then, if there are some that don’t have one, you can lend one of yours to them at the party.
Peripherals: Everyone needs to bring their own keyboard, mouse, and headphones. With larger parties, it just doesn’t work for everyone to use speakers. Make sure it’s clear that they need some sort of headset. If you’re okay with speakers, at least tell everyone to keep the volume on low.