One thing I've come to realize that really gets me down...
One of the best things you can bring for your trip to Burning Man, if you're not going full-on generator, is an inverter to provide AC power from you car. This is something that can charge your USB devices, of course (and at a higher power level), but also provide standard plugs for AC power.
If you're wondering what you might use it for, I have two words for you: coffee maker. Okay, yes, I also use mine to keep my laptop charged (writing while at Burning Man is a thing - just mind the dust!). I've also used mine to run an AC-powered air mattress pump and other random things that don't lend themselves to battery-powered alternatives. I have no memory of someone bringing a flat screen TV and feeding it from an iPad to watch sports. Nope, I'm sure that didn't happen.
No recommendation of an inverter would be proper, however, without a little background on its operation. The battery in your car provides 12 volts of DC power. Inverters take that DC power and turn it into the 110 volt AC power that you expect to find when you plug something in at home. But in doing this, it drains a lot of juice from your car's batter. In short, you don't want to use this without your car running. Think of your car like a generator - it burns gas to get you power. So especially at Burning Man, remember to pack in some gasoline to account for any time you're going to have your car running to provide power, lets you find you're out of gas when it's time for the great exodus home!
The unit I recommend, above, can plug into your car's cigarette lighter or be hooked up directly to the battery. When your car is running, it will be charging the battery while you're simultaneously using it for power. Make sure that your car's alternator is rated high enough to support the load the inverter will place on the battery. Determine how much power you will be pulling and just make sure your car can support that.
Considering that an inverter like this is cheap, it's a great thing to add to your packing list.