Beaches are always a complicated subject when it comes to talk about shooting on them.
With film you will have to have your loader out of the beach and the sand.
If you have a camera truck, unload and load the mags in the camera truck and bring them to the beach always with the case.
If you don't have a camera truck, then make production set up a place out of the beach where the loader can work comfortably and with no dangerous elements around.
Check the gate through the lens, the less you have to take out the lens, the better.
While changing mags off the beach would be something fantastic, sometimes it is not practical because of the length of the beach, times, light, etc.
If you have to change mags on the beach, make sure that the camera is covered while changing them, clean the pins very well and also the loop / metal thread.
Make sure you run a test with the "test" or the "phase" button to see that everything is working properly before saying "ok".
Don't leave anything open as sand enters through the smallest holes.
Bring to the beach just the essential things.
It would be interesting to bring a Clear / Flat filter just in case it gets super windy and you need to shoot, that way you will cover the front of the lens from possible impacts.
if for some reason your camera falls to the water and the film stock with it, get a big bucket with normal water and put everything there, sea water is the worst thing that can happen to anything and by placing the camera in normal water you will make sure that salt will be cleaned. Take the mag out and send it like that to the lab as soon as possible (as well as the camera to the rental place of course! )
On digital, all of the above mentioned still apply, however you won't have to take mags out and you won't have to thread the camera (which is something really good)
Make sure your loader, again, leaves his / her loading station off the sand.
For the cameras themselves, get a tripod and when the camera is not being used, put it on the tripod.
On top of that, get sun cream often, drink water often and enjoy a great day!
Have a good one!