I asked a cop (detective) friend of mine about this the other day after going back and forth about it on this board...here's the general conversation:
Me: hey, got a question. So let's say I'm rolling up to the gates at Coachella, a festival known for illegal drug use/illicit behavior, etc. I'm waiting in line and a cop says "hey, hows it going? you guys ready for some music? yeah, that's cool, so you have any drugs?" Will saying "no" be something that can be held against me later if it turns out I do have drugs?
Him: Not likely something that would come into play
Me: so after I say no I don't have drugs, and they ask me if they can search my car, and I say respectfully "actually I do mind, sir; I do not give consent" won't that just make them annoyed and get on a power trip and then be like "ok, so ya wanna play that game, huh? well i'm getting a dog". Aren't I just screwed at that point if I did have something?
Him: Well a) if they are going to get a dog, they have to do so in a reasonable amount of time (Illinois v Caballes), as in the amount of time it would take to do a routine traffic stop; say 15 minutes. b) yes, if they do get the dog and they hit, or they are willing to lie about it hitting, then yes, you're screwed
Me: so then why don't they just walk a dog up and down the line of cars the entire time and thereby check every car?
Him: resources. And most of them don't want to harass everyone. They JUST WANT TO WEED OUT THE IDIOTS
It may be different in Nevada, where you can utilize prostitutes, buy automatic weapons and gamble all you want, but can't smoke pot (which is obviously worse than any of those other three), but here in Cali, they have other things to do. Some hipster smoking a little chron isn't really a concern to them. Same with massage parlors. They want to bust murderers, drug traffickers, domestic violence, rape, kidnapping, etc.
So like others said, best bet, obviously, is bring nothing. Next best bet (since the idea that no one out there has anything is a bit silly) is to not be an idiot. Arrive sober. Have your taillights and headlights (or is it lamps? i got yelled at last time) working. Don't block your license plate. Dont have illegal things sitting out. Don't have an overpacked car. Wear your seatbelts. Be respectful. And (in my opinion) it might not be a bad idea to wear lame (i mean normal) people default clothes until you get on the Playa, or at least to the greeters. I plan on showing up in a clean minivan dressed like the good suburbanite that I am. Hell sir, good day sir, we are actually here to document this most unusual of social experiments for our college newspaper. Oh yes, that is a Bush/Cheney sticker on the back. We love those darn guys, don't you? Oh, sorry, is my NRA sticker partially obstructing my license plate? Goshdarnit, I'll fix that just as soon as we get to our camping spot.
Please forgive me...this cubicle has stolen portions of my mind and my soul