Remains one of the few contexts where nerds would do drugs. Speed mostly. You ever played Quake with a bunch of dudes on speed? It's fucking nuts.
The smells. Some LANs would go on for a week. Lots spanned several days, most lasted upwards of 12 hours.
People didn't game with laptops. You had to bring you whole case, your monitors, accessories. It was great when LCDs came about. Lots of people had intricate setups too, heavy Thermaltakes with watercooling shit.
ICQ, AIM, MSN Messenger and that annoying Windows service that let you send pop-up messages to any IP if you hadn't disabled the service.