Reddit mentions of Kool-Aid Singles Tropical Punch (for 16.9-Ounce Bottles), 12-Count Packets (Pack of 6)

Ok, so the camping area and the music area are separate and they don't allow you to bring in booze to the music area. Drinks are crazy expensive in there too and it is a drag walking all the way back to your campsite if you want to get tipsy. Not to worry though, it is very easy to bring in booze. You are allowed to bring in one sealed water bottle or one empty water bottle/nalgene (there are free water stations all over in the music area). So use these to make yourself some sealed water bottles that are actually full of vodka. Have a friend bring in an empty Nalgene and toss some of these in the bottom of your bag. You are now equipped to get drunk without spending a fortune on drinks. This works at virtually every festival where they do not allow you to bring in outside alcohol. I did it at summercamp with a whole case of these stealth water bottles.

EDIT:I forgot some things. Pack rubber rain boots and an umbrella. If it rains, festivals get MUDDY. This year Summercamp was totally rained out, but I was still able to enjoy it to the fullest because I had my boots and umbrella. So many people left early because of the weather. EF is car camping, so you don't really have to carry anything on your back into the festival, so you might as well fill the car up with everything you need without worrying about weight. Also on the way in they will ask each car if they are in a caravan so that those cars are kept as a group and everyone will be camped next to each other. If you guys are taking more than one car I would highly recommend not camping in a huge big group. My best friend and I went this year and while we knew other friends that were going we didn't try to camp near them. Best decision ever. Going with one or two other people instead of hanging out in a big group of people you already know is awesome. I didn't go to EF to hang out with people I can see every day. I went to meet awesome new people, like our neighbors. Pack a hammock. ENO puts hundreds of hammocks in the forest, but they get taken rather quickly. Bring your own in so you can chill in the forest when it is hot or between shows.