Aside from a 4WD-ready vehicle, here is the bare minimum you need to have.
Before heading out, be sure to check over the vehicle thoroughly. Check the oil, fluids and gages and look over all hoses and bolts.
Make sure you have a spare tire and jack, extra fuel, and a basic tool kit for vehicle maintenance and repairs. It's also smart to have something to clear trails with, like a chainsaw, hand saw, or axe. A spare key might also be a good idea.
Plan on getting stuck. Pack tow straps, a come-along, and a shovel. Other straps, like ratchet straps, chains, or ropes can be versatile and useful too.
This is a good time to stress the importance of traveling with a buddy so there are multiple vehicles around should someone get really stuck.
If recovery fails, you need to be prepared for staying overnight, if you already aren't planning to. Having a radio or cell service-free phone to contact others is important, as is a compass or GPS unit.
Make sure you have a complete first aid kit, emergency blanket, firestarter, a flashlight, and plenty of food and water.
If you are planning on camping, you'll already have things like a tent, tarp, sleeping bags and essential medication. If you don't already have these personal supplies packed, throwing them in could be the deciding factor in a safe or life threatening 4WD adventure.