A backpack was the first must-have. Since you'll be on the go pretty much the entire day, it's easy and roomy enough to toss all your essentials in along with some potential purchases you'll make along the way. No body wants to jam pack Tetris style constantly in a little fanny pack or lug around a shoulder purse.
A bandana is on trend and a key accessory. Equally adorable around your neck or in your hair.
Sunglasses (duh). I don't recommend taking your brand new Ray-bans, but an easily replaceable inexpensive pair. Heart sunglasses are simply sweet for soaking up those festie sun-rays.
Sandals: consider comfort and walk ability. You're going to be walking miles a day, make sure your feet can handle it.
A cute dress. There will be a time throughout the festival that you will unfortunately most likely need to use a porta potty, it's the nature of the event. Wearing a dress makes getting in and out of those disgusting hell holes a breeze. Also, you don't want to wear something you're constantly tugging at to adjust, falling off your shoulder and so on.
Overall: Keep to the essentials, easy, and no-fuss items. Are you heading out to any festivals in the near future? If so, which ones? Here is where to find all the items listed above: