Second the fanny pack with critical gear - ID, cell phone, meds, sanitizer, flashlight, TP (mission critical). There are no 7-11's handy so triple spares of glasses, meds, disposables, sunscreen, personal FAK/ toiletries.

This is a guess from far away but I suspect that most people going to an event will be spending the nights in large camps with other rescuers. From that I would guess that there will much of some stuff and critical shortages of other stuff.

What I might pack for working "in camp."

wet wipes
unique looking bottle/ mug for water
flasks of non-water beverages
batteries, them more.
solar/ crank charger for whatever electronics you are carrying.
locks for your gear
cash
jumbo repair kit
music player
plastic bags/ boxes ( dust)

It is a hot dusty environment. expect to be outdoors/ semi outdoors for weeks

sunscreen
sunglasses (case) spares / wipes
hat
chapsticks


trade goods: ( for your team)
any chocolate that can take 95 degrees
pens
tiny snacks of any kind( powerded drink mixes)
earplugs ( box)
any sort of caffeine


Again, these are guesses - but might be a good place to start

TRO