When driving to Terlingua, make sure to download offline maps on your Google or Apple Maps app on your phone. There are long stretches with no cellular signal on the way to Terlingua and inside the park as well.
Fuel Up
Make sure you have enough fuel in your vehicle at all times. If driving from Austin, Houston and San Antonio, there is a roughly hundred-mile stretch between Ozona and Fort Stockton with no gas station. Also, there is no gas between Alpine and Terlingua (85 miles).