Let's see,

My new straw cowboy hat (this is a country musicathon isn't it?)

Lawn chairs (we are a tad too long in the tooth to stand 12-14 hours), maybe a small tarp to lay on too

Ear plugs

Sunblock

Sun glasses

Mini-binocs

Something in case of rain/cool temps (you didn't say how high the elevation is)

Couple of boxes of Travel-Johns, and a Lady-J for my wife (they never have enough porta-poties, and sometimes ya gotta go NOW)

Food/muncies and a rolling ice chest with drinks (who wants to stand in line forever and pay super high prices). If allowed. Trash bags, at least for your own trash

Camera/camcorder (if they will allow them, some don't. Try to find out in advance, hiking back to the car to put cameras in the trunk is a pain).

FAK of course

No blades (some concerts they search you, again you want to avoid that hike back to the car)

A good mood and lots of patience. Spending 14 hours in the sun along with a jillion other fans, many drunk, can be a little hard on the nerves...