Still, there's a short list of ingredients that can ease the process. Ground clearance, or ride height, is probably the most important -- the higher your car or truck is off the ground, the greater the chance you have of not getting stuck. Next up is rubber -- you can cross Africa on street tires if you've got enough experience, but for the most part, sidewall flex and soft, knobby rubber are your friends. Tires that give when they encounter an obstacle are less likely to puncture or tear, and as a side benefit, they'll also provide more grip for climbing over slippery or uneven surfaces.
Lastly, don't discount torque or suspension talent. The same qualities that can help make a vehicle more pleasant on the street -- grunt when you need it, regardless of rpm, and a healthy dose of pothole-friendly wheel travel -- can also help it tackle the wilderness. A lot of off-road driving is spent at single-digit speeds and high loads, and big throttle openings are rarer than ice cubes on a New York sidewalk in July. The instant-on shove that comes from a torquey engine helps you claw over obstacles and inch your way out of (or into, if that's your thing) nasty, slimy situations. Things like locking differentials, traction control, and adjustable-height suspension will boost the number of places you can venture, but they're not a vital part of the experience.
In short, if a car looks like it might be decent off-road, it's probably safe and capable enough, presuming your mechanic gives the OK and you pick an appropriate trail. Pickup trucks with big tires, SUVs you have to climb into, even some all-wheel-drive cars will work. Keep in mind, too, that the U.S. Forest Service (USFS) and Bureau of Land Management (BLM) rates most of the more popular off-highway trails in the country -- their ratings mark the difficulty and equipment required for a given road, and they're as good a guide as any. When in doubt, err on the side of easier trails, a shorter wheelbase than you think you need, and caution.