Heading from east Texas if on Hwy 90 you can stop at Seminole Canyon State Park and see the pictographs, visit Judge Roy Bean's at Langtry, Texas. As mentioned Marathon Gage for food. At Alpine, Texas Sul Ross has a great little museum on west Texas History and it is free. Head south on 118 to Study Butt which has a good RV park, food and fuel just 2 mile from the Big Bend entrance. The risk is driving down into Big Bend and not getting a site. Good central spot to satellite out and see the surrounding region. We always drop the RV at Study Butte and hit all the back roads and surrounding towns in the Big Bend area. From there you can back track to Alpine and stay on 118 to Ft. Davis State Park and see all the sights in the region there. Marfa is only around 22 miles south on Hwy 17, McDonald Observatory 12 miles from the State Park, do take the scenic drive around the mountains. From Ft Davis you can head northwest to Van Horn, Texas and Hwy 54 north to Guadalupe Mountains National Park, camp and take a few hikes, east on Hwy 62/180 see Carlsbad Caverns and across the corner of New Mexico (become Enchanted) to Seminole, Tx to Hwy 385 north to Lubbock, Tx where you can head north on Hwy 87 to Canyon, TX were you will turn east to Palo Duro Canyon State Park and or Caprock Canyons State Park and see the buffalo herd.
You will be in scenery overload by this time.