Background: The first in a series of my system for going to shows, usually of the outdoor or late night variety. I've been to probably 50+ at this stage and have refined it to a process.
What to take
Keep items in your pocket to an absolute minimum. A $20, some $1s for a vending machine, and your ID. I wouldn't even take my wallet. Make sure keys are attached to you in some format (D-ring / or whatever).
Take a cheapy flashlight of some kind with you. SO many times I've been in some dark area and someone dropped something and phone light was just NOT enough to see it. Or stuck in some back hallway or a dance floor where you just couldn't see anything. A flashlight is a great signal to get people to move out of the way if you need to leave quickly and it's also a great way to get the staff's attention if something's genuinely wrong (e.g. someone passes out or gets a bloody nose on the dance floor).
If you must take a weapon of any kind, make sure it's of the very small variety e.g. a tiny Swiss Army knife things with a blade that's as low key as possible. Ideally carry something that looks like a pen.
Next: Part 2: Dress