Speakers, at least 6 (2 each of subwoofers, mids and tops). Preferably many more. Say, about three dozen total. JBL, Cerwin-Vega, PAS are popular brands, as is the Carvin Pro Audio line. Rent the large rig, own your own small rig, unless you're just drowning in expendable cash.
Audio power amplifiers. Generally 1 each per subwoofer at about 1000 to 3000 watts in 4 ohm bridged mono mode. Generally 1 each per pair of mids and tops in the same range. QSC and Crown are popular and reliable brands. Avoid Carvin amps. Avoid anything that says "American DJ" on it, be it amp, mixer, or blinky light.
Effect and processor rack consisting of at least: 16 band stereo parametric EQ, digital delay/reverb processor, BBE Sonic Maximizer, model 882. (The BBE is practically essential, especially for bass-heavy rave-based sound reinforcement.) Mixing board for multiple DJ rigs or live PA work optional but recommended.
Cables, a metric fuckton of. Power cables, extension cords, power strips, breakout boxes, snakes, patchbays. Speaker cables in Speakon, banana clip, quarter-inch tip-sleeve patches, all in beefy gauges with clean connections. Audio patch cables in XLR, quarter inch, RCA stereo pairs and even 1/8th inch miniplugs. An entire zoological catalog of adapters, mating reversers, RCA barrels. More patch cables. Raw cable and parts to make or repair cables.
A DJ rig consisting of at least two Technics 1200 MK-2 turntables, self-powered monitors for the booth, and a decent 4 channel mixer with an assignable crossfader, tolerable cue and monitor controls and booth-level auxillary functions. A CD DJ rig is optional, but increasingly common. This rig may be contained in a unitized and armored "coffin" or in seperate ruggedized travel cases. Some sort of stand or table is mandatory, and that folding chipboard conference table is just a ton of bad news in the form of turntable feedback and bump-related needle skippage just waiting to happen. Suprisingly, industrial strength saw horses with a 3/4" to 1" plywood topper are fairly common.
Blacklights, blacklight artwork, gel lights, cans, gimbles, gobo lights, pinwheels, oil wheels, video projectors, film projectors and film loops, intellibeams, TEMoo multiline full spectrum argon lasers, optics, scanners, strobes, more blacklights, DMX controlled chasers, DMX controlled anything that goes blinky-blink. Much of this is optional. Real raves just need sound, space, and people.
Assorted hand tools and power tools. Soldering iron. Solder. Wirestrippers. Pocket knife. Leatherman multitool. Flashlights, preferably 3-6 D cell Maglights for durability, brightness, and fending off saucer-eyed cable-eating zombies from Mars. Headlamp. Small flashlights in pockets, on keychains, on zipper pulls. Toilet paper and/or paper towels. First aid kit. ABC rated fire extinguishers. Generic megasize bottle of ibuprofen. Ear plugs.
Duct tape. Gaffers tape. More duct tape. Warning tapes. Traffic cones. Flourescent tape. Electrical tape. Masking tape. Pens. Markers. More duct tape.
Medium to large spark-arrested and muffled generator with spare filters, plenty of spare jerrycans of gasoline, and assorted spare parts for outdoors. OR illicit stash of lineman's tools for those essential last-minute power hookups (Don't do this. Seriously. Just don't.), including assorted fuses and breakers.
Cold beer. Lots. No, that's not enough. More. Trust me. And a cooler with ice.
Cigarettes/cloves/tobacco of choice. Lots. Listen, smartass, what did I tell you about the beer?
Water, snacks, and assorted sustainance materials of choice. Again, lots.
Folding chairs. Spare socks, t-shirt, and underpants, clean. A clean towel or three. A large tent for outdoors. At least one shade structure capable of protecting the DJ and sound rig for outdoors. Spare batteries, lots. More duct tape, beer, water, food and tobacco stuff. Spare flashlights or bulbs. Rubbermaid totes, duffel bags, or milk crates to put everything in. Spare needles for the turntables. A siphon or pump for gasoline for when the tanks run dry and you start cannabalizing the gas in cars. Spare everything. The party must go on.
Despite what some wannabe rockstar DJs will try to convince you of, finding good DJs are never, ever a problem, and can always be found in droves the instant you set up. You don't want rockstars, anyway. You want shamans to lead you to the promised land and scry the depths. (Just this last weekend we started an outdoor with only 4 confirmed DJs, and we went non-stop for almost 2 days without ever repeating a single track. No problem.)
And most importantly: A great attitude and an inexplicable desire to attempt to make a shitload of people incredibly happy for a few hours (or days!) in exchange for very little tangible reward.
...of course, having someone on hand with an intimate understanding of how a TAZ works and a Jedi-like ability to make the authorities go away quietly is a major plus...