Dessert sand?
Others have mentioned a lot of good advice. I'll add a few things.
1. Safety in (smart) numbers. Qualified and experienced off road drivers
2. Minimum 3 vehicles, each able to pull the other 1 on 1.
3. Each vehicle carries recovery and survival gear.
4. Each vehicle sufficient condition and space to carry ALL PASSENGERS in an emergency. Know what stuff you might need to keep with you in case of injury/danger bugout.
5. Fluids. Water, trans fluid, oil, fuel.
6. Know WHEN to abandon a vehicle. Expensive tows or long recovery hours with help is a whole lot better than life-threatening survival mode ;)
7. When possible, try not to be the smartest, most experienced, or best prepared person on the trip. If you can bring someone who knows MORE, do it ;)
8. Be medically prepared with supplies and gear. I've set joints and done minor surgery (to avoid potentially life threatening or permanent damage) on survival style trips, recently in fact ;)
9. Bring your Can-Do, Let's-have-fun attitude and leave anyone without it at home ;)
Have fun!