Just some bits and pieces based on past Lans. I'll update if I think of anything else.
Gang Adapter: Bring it with you if possible. You know, the 3pin multiplug thing you use to plug your monitor, pc, speakers etc into the mains.
Sleeping: people can sleep wherever - there's the main room with the PCs and a few smaller side rooms. Camping is usually quieter & more comfortable so bring a tent along if you want the choice. If it does turn into a biblical flood you can always stuff it in a corner and sleep indoors!
Update you games!!!: do it at home before you leave. Spending the entire of Friday evening watching progress bars while everyone else is playing isn't fun
Kitchen: the kitchen has...microwave, oven, range cooker, ice machine, toaster, fridge, plates, mugs, glasses, cutlery and most importantly a sink

. If you are cheffing it then it's worth bringing anything essential like bowls, pans and knifes etc. Seem to remember the kitchen has them but they're really weird sizes.
Tea, Coffee etc: There's a big box of tea, coffee and squash. Help yourself. There's usually a loaf and spread around too.
BBQ: they'll be one over the weekend providing it's dry ish. If you're a veggy then let us know what you'd like or bring your favourite with you.