Howdy Fellas:
I won't be there with you. But, I've been out there and out many other times and have some suggestions.
Ear plugs beside's muff's, take extra's there's always other that forget theirs, or muff's that break etc.
Shooting glasses will keep blown primers and the wind from burning your eyes a lot. Nothing as miserable as windburned eyeballs. Take a bottle of Saline solution for contact wearers. It's only a buck a bottle and will sure be appreciated by anyone with sore, dry eye's, or when the dust blow's grit in them.
On windy and sunny days a light screen type headcover whether it's camo, or just a bug type will cut the wind and sun and should let enough breeze (hehe) thru to help cool you off some under that big brimmed hat. Lots of place's are infested by knats too. Some clothes pins are real handy to have along. Clip the back of the hat brim to your shirt collar to shade your neck is one good use.
Sunscreen the back of your necks, hands, arms and some will be in shorts so the legs will need it too. Wear boots for the cactus and rattlers.
With that many rifle's along, why not rig up a standing gun rack?? Open the bolts and stand them in the shade.
Couple buckets, one for loose ammo and the other for empties. Even rimfire's, lot's of ranchers don't like to find pile's of brass. It's easy to drop them in a bucket. Collect them all you can and one of the local guys can sell 'em for scrap, brass price's are nearing a buck a pound now. That many shooters might fill a bucket with split necks, scraps and rimfire brass.
Take a soft mat to lay on too, after several hours setting at a bench most of us are ready for a nap, or at least a few minutes laying in the shade. Right?
Drinks, make sure you take 4 gallons per person per day, AND drink it ALL! Cool is much better than ice cold for your system too.
A good sweat band will keep the salt water from your eye's, just take it off and ring it out now and then. They are 2/$3 or less.
Long sleeved light colored shirts, or light tan is a good color, pants to match work well. Bright white will blind others in the sun, and darker colors will cook you whether in the direct sun, or not.
I like to use a bipod. It works just great when sitting on the ground. Take the legs off a cheap plastic one piece chair. They are slicker n H to sit on the ground. Perfect height for a bipod, you can lean back in them and have back support, or tilt way back and it's nearly like sitting in a recliner. I've got one with shoulder straps all painted camo colors for coyote calling. Sure am pleased with it. Even in snow, it keeps my butt dry, keeps me off the cactus and unseen stickers too. With a couple bungy cords you can load the seat with a small cooler and/or supplies, or a couple dead coyotes wrapped inside garbage bags as we do. Takes a partner to help you stand up when loaded though. Whole lot easier than carrying things in your hands. Make sure to take a tall can of flea spray too. Never know whether you might get into them. Sure don't want to get sick from flea bites, might prevent the plague too. It's cheap insurance.
Don't drive all over the pastures, that will kill the grass for years and ranchers sure don't like that. Stay on the tracks and walk to the shooting positions.
Keep in mind, ammo loaded hot, will/can blow a primer, or gun up when the shell's chambered in a hot gun for several minutes. IF your next shots going to be awhile, don't chamber it, leave it in the magazine. It'll help keep your gun cooler too as the heat will draw a breeze thru the barrel when it's open. Pace your shots, there's nothing gained except burned barrels when making rapid shots. One or two shots a minute is plenty and you'll still probably run out of ammo before the days out. Make it a habit to only chamber a shell when your ready to fire, then eject the empty soon as it's fired.
Prairie dogs are not going anywhere more than 50yds from their mounds. So there's no rush to get more shots off. Take your time and they'll be around when you're ready to shoot. Many times they won't pay much attention when you shoot high over them, so leave the close one's alone for later shots and shoot the further one's first. They won't panic as bad this way.
It's always fun to know how many hits you make. IF you use ammo boxes, place the empties up, and hits down. OR take a note book and mark it. Lot's of fun to compare notes with the other guys. My best has been 98/100 many times. Some days 400 shots a day at the same %.
Good luck, stay safe and have lot's of fun.
George