My headlamp also uses 3 AAA batteries, but it is regulated so i can use lithium batteries, which last a lot longer. For short trips, I keep track of how long the batteries have been in. For longer trips, I put in a new set for the trip, and they last longer than even a 10-day trip--they would work fine for at least 14 days. The only extra batteries I carry are a set for my camera. BTW, I see no mention of a camera or of any navigation device such as map and compass.

Do you have bugs in Texas? I see no mention of bug netting or a headnet or bug repellent--I would think you'd want at least one of these!

Of course I may have missed the above. . . .

You'll need more--and larger--water containers for the Hayduke Trail. Remember that Platypus are not compatible with Sawyer Squeeze. Look for Evernew, which I believe are now, finally, available again. My own experience with the Sawyer Squeeze is that you definitely want those backup tablets!

You might want to test out that whistle with a friend. I gave my grandson an REI whistle a couple of years ago. When he sprained his ankle, he used it, but I only heard (from about 200 yards away) something sounding like a sick bird! He finally yelled, and that I heard distinctly. It's supposed to be the other way around!