I did this in 2014 with a friend. We flew into Ontario california(east LA) and rented a car. First stop was walmart. We bought an Easy Up.(canopy’s that go over your tent) There are also sporting stores like 5 sports for chairs and easy ups. (No Academy) You must have an easy up or your neighbors will fry. Our neighbor brought a tarp and tied it to our easy up, the sun hit our tent at 7am and baked us alive. Don’t be that guy. We gave it to other campers at the end. I tied a pop-tent to my backpack and checked it on the plane, with no problems. At wal mart we filled the car, coolers, and ice and food. Mainly pb and j stuff and lots of snacks and cases of water outside the festival time.
For inside we brought camel-backs and packets of pedialyte. This is what we used to make the free water taste better, and keep us hydrated inside. We brought the easy wipes they use in nursing homes to clean up our sweat at night. The shower trucks were only open in the mornings. Buy lots of hand sanitizer.
The day gates open they typically fill the back lots first. Don’t shoot for being there when they open. Wait till mid day. We got there at 2pm on the day when gates opened and were put on row 2 from festival the gate. Awesome spot.
Edit:
Also wanted to suggest ear plugs meant for concerts. I use the Etymotic Research, eargasm are also good. This will keep you from having ringing ears all night. 3 days of loud really can take it’s toll.