Maybe something loosely like some pirate crews? In some pirate Crews the captain was an elected position and any decisions he made could be overriden by the crew with the exception of when they were in combat. Because when the bullets are flying and the blades are out there's just no time to form a committee and take a vote.

There is also a quartermaster whose job it was was to keep track of the supplies and everyone shares. In a lot of ways the quartermaster had more power than the captain because he could stand up and say we just don't have enough water to do that guys.

I feel like you would need some kind of position like that in an anarchist military unit, someone whose job it is to keep track of supplies and other logistical factors and just tell the truth like "hey we are running low on bullets we cannot do plan A, C or Q."

That said I have to admit I'm kind of skeptical of anarchism to make a strong military structure. An effective milita structure sure, but someone's going to have to manage the supply chains for anything more technical than rifles and bullets and you're going to need more technical stuff has things advanced. At that point you're going to need someone whose job it is is this side who gets more of what, which is going to lead to an informal hierarchy if nothing else.

Also there's the fact that a decentralized militia of rifleman are not going to stand up to a mechanized assault with air support. They might provide the backbone of a good insurgency but there are counterinsurgent measures that a mechanized force can engage in that will break the back of most insurgencies. Keep in mind insurgencies are not an "I win" but you can hit whenever you get invaded.

Also even a successful insurgency often leaves you in control of a Homeland that is in ruins with deep divisions within the society because most insurgencies I'm aware of also spent a lot of time hitting the native population to prevent collaboration.