All supplies should be brought in if not for the mere fact that obtaining supplies in the region can often be pricey. Remember though, the desert can be a desolate and unforgiving land, always bring more than you think you will need. Campfire BBQ's and fresh fruit are certainly treats for which you will develop a new found appreciation for. And typically, as Car Camping is the desired approach, you can feel free to bring in almost all that you need.
A couple of suggestions for meals:
Cereal and milk
Oatmeal (for cold mornings)
Coffee or Tea and 'greens'
Sandwich with plenty of nice cold veggies like cucumbers and tomatoes.
BBQ chicken, pork chops or steaks
Bell peppers, onions, zuncini, tomotoes (best prepared in a covered tin)
Corn on the Cob and either regular or sweet potatoes(wrapped in foil and placed on the edge of your fire)
A hearty soup
Beef jerky and the road also go well together as long hours on the journey need a bit of flavor. Notable is a small shack on Interstate 395 simply named 'Fresh Beef Jerky' in Olancha. Its $20 for 3 packs, but its fresh made and quite frankly the best jerky around. There's plenty of pickled vegetables and free samples also.
Bring plenty of water. A standard rule of thumb is 2 gallons per person per day. Of course this can be partially substituted with fruit juices or sodas, but make sure that you have more than you think you'll need, particularly if its your first time venturing in.
The desert can be a brutal and unforgiving place, you should be prepared to be fully self-reliant particularly if you are planning to go camping
Since proper hydration is a major concern it is recommended to follow the general rule of bringing 2 gallons of water per day per person.
Drink even when you do not feel thirsty.
When hiking, carry a gallon of water for each day plus extra in case of an emergency.
Store extra water in your car.
Carry water even if you are only planning to explore a short distance from your car.
Dress for Success
Wear a hat with a brim and light-colored, lightweight clothes.
Pack warm, wind-proof clothes in case the wind picks up or the weather cools.
Wear sunglasses and sunblock, lots of sunblock.
Carry a Flare & a Spare
Ensure that your car is in good working order - service stations are few and far between.
Carry a spare, a jack, and some flares.
Carry boards to place under tires in case you hit a sandy trap (see below).
'Fix-a-Flat' can be a lifesaver along with jumper cables.
If You Hit a Sandy Trap...
Shift down and keep moving.
If you get stuck, do not spin your wheels; it will only dig you in deeper.
Try going in reverse.
If going in reverse does not work, place boards or carpet scraps under your tires.
If you cannot get out, stay with your car.
Do not leave your car unless you are certain that help is close by.
Know Where You're Going
When hiking, always carry a topographic map and compass.
Take a compass reading before beginning your walk, and look for landmarks to guide you back.
Let someone know where you will be and when you will return.
Pay attention when traveling back roads; they often branch and divide.
Avoid flash floods by keeping out of narrow canyons and washes when there is a chance of rain.
Abandoned mines may have hidden shafts, and old buildings in ghost towns may collapse; be careful.
Gas: when the sign says "Next gas 50 miles," you better know you've got enough to make it before you pass the pumps! Never go lower than a quarter tank.