On a well run event you have "net control" which is basically a central point that you pass messages to and they pass them out. They're usually an experienced ham set up with a good antenna, and a reasonably powerful transmitter, at a location that can hear from and speak to everyone even if people with handhelds can't hear each other because of distance or terrain. There's a convention for getting permission to speak and how messages are conveyed and passed on.
In my particular case, we set up an antenna for ham frequencies and public service frequencies, officers from our town are deployed, and can talk to us on their police radios but frequently can't speak with each other because we're not in our home town and don't have our repeater (other towns use other frequencies). So I relay messages between officers and I relay messages to and from net command.
Also, if you think about what happens when an emergency (like the Boston Marathon Bombing) happens... imagine how much slower and more disorganized the response would be if all the departments had to make cell calls to each other and wait for each to get off teh line... the central point would call one police dept. Then they'd call the fire. Then they'd call.... and now people are dead because you can't communicate with more than one person at a time.
it's just WAY more efficient than cell phones.
We normally have somebody free who can travel to any field station if they have equipment problems etc.
Most events pay a small fee for our help, which goes to the local club.
What I mean by "a stack of radios" is at the two races I've marshalled that had radios, they had half a dozen license-free walkie-talkies like [1] which they handed out. The "stack" was figurative, as they wouldn't have stacked up very well.
I assumed you'd be the only license holder and you'd somehow co-ordinate between the license-free radios. If you could get half a dozen license holders, obviously it's a different matter!
(The license-free radios didn't work at either race)
[1] https://www.radio-solutions.co.uk/motorola-walkie-talkie-xt1...