I would emphasize a point made earlier - the fit of your backpack is crucial. I would recommend carrying a loaded pack on day hikes to get comfortable with the experience.

I think most of us acquired our backpacking expertise by going from day hikes to gradually longer backpacks, adjusting our gear and looking for lighter weight alternatives as we learned what worked for us. It is all about the three B's - backpack, boots, and bag - once you get those dialed in, everything else will fall into place.

From what I have been able to read, Big Bend does not have the border incidents to the extent that the Arizona parks, especially Organ Pipe Cactus, do. It would be instructive to hear from others on this....