Leave the "large battery" for recharging home. Turn your phone off except at the top. It won't work anywhere else. Camera battery should hold enough charge to take all the pics you want. Don't waste battery by viewing lots of pictures "just for fun".
Your iPhone works as a backup light. You don't need two backups. Headlamps don't need replacement batteries these days.
Wear the old boots. Nicely broken in works better.
