2- Check the Tires - Check the condition of your tires, including the spare. Be sure they are all inflated to the proper highway speed pressures. Take note of your tread and think about the terrain you will be traveling on. Are you ready for that deep mud hole with that tread?
3- Ball Joints - Check all your ball joints, tie rods ends and wheel bearings by jacking up and securing the front of your 4x4. Grab the tire by the and at the top and bottom, and check for any excess movement by rocking the wheel in and out. Do the same by rocking the tire side to side. Any excessive free play should be checked out by a qualified mechanic. Also check the rear in the same manner. In solid rear axles you're checking for worn bearings and other damage.
4- Plan the Trip / Inform Others - Tell those that should know where you are going, when you are leaving and when you’ll be back. Let them know when they should start to worry about you if they haven’t heard from you. Give them contacts in case they need them. Prepare your trip. Have a map of the area you are going to and how you should get there (and home again).
5- Weather - Watch the weather for the region you are visiting and the route along the way. Be prepared with the appropriate clothing and protective gear (rain jacket, hats, sunglasses, lip balm, sunscreen). Pack extra clothing in case you get wet or it gets a little colder than expected. Even if you are not "planning" to stay the night, its good to have a sleeping bag. Its better to be over prepared than under prepared.
6- Communications to the World - Pack a cell phone and give it a full charge before departing. Pack the phone car adapter. When you're remote and offroad, you can still find a signal even if its atop a ridge or up a tree. Be aware that if your are out of signal range, your cell phone will be hunting for a signal and this will deplete your cell phone's battery quicker than just sitting in standby when in range.
7- Food / Water - Bring plenty of food and drink. Even on the short trips. Bottled water, energy bars, and dried fruit, sports drinks, anything that has compact energy are good items to pack. Pack items that do not need refrigeration. Avoid salty foods such as chips, unless you have plenty to drink. And no, beer doesn't count. In fact it takes water to metabolize alcohol so the beer and liquor will dehydrate, not hydrate you. Alcohol is never a good idea when you have to think clearly.
8- Top off the fuel - Fill the fuel tank prior to every trip. When you reach your destination, top it off again before hitting the trail. The last thing you want to do is start worrying about running out of fuel while offroad. Remember the One-Third/Two-Third Rule: Use one-third of a tank to get where you are going and save two-thirds for getting out. If your fuel tank doesn’t have the capacity for the offroad portion of the trip, carry extra fuel or re-think your route.
9- Jumper Cables - Have a good set of jumper cables with heavy-gauge wire and quality connectors.
10- Belts and Hoses - Check all your belts and hoses, and carry spares. The lower radiator hose is the one that usually gets damaged while off-roading, so ensure that you have a spare. Alternator/water-pump belts are the most important. Newer vehicles often use serpentine belts. While much less prone to failure, they can be difficult to change. The are also expensive, but carry one. Replacing an old serpentine belt and saving the original as a spare is a good idea.
11- Jack - Make sure you have a working jack and know how to use it. A High-Lift jack is a great universal tool and also doubles as a come-along (and lots more).
12- Tool Kit - Carry a tool kit that covers the basics of your vehicle. Carry a well equipped first-aid kit. Carry an emergency kit that covers situation beyond first aid. This might include special medication, poison ivy treatment, etc.
13- Flashlight - Carry a flashlight and an extra set of fresh batteries
14- Blocks of Wood - Brink a few scraps of plywood measuring about about 10 to 12 inches square. You may need them to support your jack if you have to change a tire on the uneven ground. 2x4 or 4x4 blocks also come on handy.
15- Lights and Markers - Make sure you headlights, taillights, and brake lights work.