No drinking on the sand. If you must, just have it in some non-descript container and you should be fine.. I've
only observed this in the past

I was ticketed at DuneFest once in the half dozen times I've been. We were staging out of the 3rd parking lot.. and honestly it could have happened at any other time of year. But on the sand you shouldn't have any issues. Just be smart if you see Ranger Rick. "Sand Camping C" is typically where all the drag racers camp so no worries about noise violations in that area.
They do give complimentary sound checks which should prevent a ticket at that time. But, if you fail, they'll likely ask you to leave. So next time I'm trapped, I'll likely wave at Ranger Rick and ask for a complimentary sound check to forego the ticket. All that being said, I've been stopped 4 times in all my years riding the dunes and was only ticketed that once. YMMV.