I am a big time coon hunter. I absolutley love it. Here are a few tips for what youll need. Not sure if you brother will have all of this or not but it will come in handy.
1.) A good flash light, ( If he doesnt have coonhunting nite lights.)
2.) Deffinently want to wear water proof boots, ( If you hunting around any water...Coons travel frequently along water. Creeks, Ditches, Colverts...etc)
3.) Water, His dogs may tree one within the first hundred yards or maybe a quarter mile away. You never know, It also depends on how well the dogs have been trained. Your gonna get thirsty lol
4.) As for a gun, I would stick to a 22 lr, or 22 mag... (depending on if he is going to skin them out and tann them for the fursales... Im not sure if he traps or not, but the value of the pelt goes down with the more damage on it. )
Most of all have fun, Coonhunting is one of my favorite past times... BTW what kind of dogs is he running if you know.... I hunt Black N Tans and Redticks.... Best of luck to you!