If you enter the park from the North as I did your first stop should be the Persimmon Gap Visitors Center. Here you can get a map of the park, other information to help you plan your visit, and discuss your plans with the helpful rangers. You can also look over the informative displays about the area and its wildlife and plant life. If you enter from the West then you will have to drive about 30 miles past the entrance to the Panther Junction Visitors Center.
You can go to the Visitor's centre which is useful and informative, I bought a postcard for VT member SL Liew to add to his collection and tried to telephone hubby, with no joy. Can't work the US phones for love nor money. The various boards and exhibits off the main road tell you about the ancient swamp creatures in the Eocene period, animals that lived in the rivers and streams and the many fossil bones dug up here.
You can go and see the Rio Grande which has a host of wildlife, herons, beavers, turtles etc and you can kayak or canoe along the river if you want to. Camping is also available at designated sites along the river.
Before you leave for your long drive to the park, make sure that you have packed LOTS of H20! Hydration is very important due to most of the park being located in the desert. Camel packs, water bottles and first aid kits are very important while hiking.
Also, make sure you research your camp site before you arrive, some may have water but others don't.
The best way to shower is by purchasing a solar shower, leave it out during the day for the hot blazing Texas sun to warm it up and shower at night.
Terlingua is also a lot of fun, so if you have some time and want to meet up with civilization again, check out the Starlight Theater and the Boat House Saloon.