Beyond what has already been listed, I would also plan on bringing everything necessary if you had to spend the night. You never know what can happen on a trail and despite having everything that you think you'll need to fix your 4Runner or get unstuck, there is a slim chance you will find yourself sleeping in the back of your 4Runner under the stars. This happened to a member here a few years ago.
http://www.toyota-4runner.org/3rd-gen-t4rs/55150-red-cone-recovery-9-21-a.html
I always take extra clothes, a jacket, a couple of MRE's and plenty of extra water! I can't emphasize the water enough. Even on day trips when I think I've packed plenty, I still find myself drinking it all. I also leave at least 3 things in my 4Runner at all times in order to start a fire. I have a lighter, wind proof matches in a water tight container, road flares, and a FireSteel (
FireSteel.com - Best FireSteel) in my 4Runner. I also have hand sanitizer and a roll of TP to help aid in starting a fire.
Not to bring up a taboo subject, but I always bring a firearm with me when I go wheel'n as well. If you can legally own one and are trained to use it, I would highly recommend bringing one. You'll most likely be outside of cell phone range when you're wheel'n and it's not just the 4-legged predators that you have to worry about if you have to spend the night. Just something to consider.