I've had the express privilege of spending some time in, "the pit", a mysterious space that is both exciting and excruciating. There are no hard and fast rules for preparing to shoot in the pit (there are rules) and there is no denying that every event presents a unique experience. There are, however, a few things you could do to ensure a more enjoyable experience...
PRE-GAME: Confirm that you have not only been approved for a media pass but that you have the necessary pit pass(es) too. One without the other is quite useless. Double-check which areas your accreditation and passes grant you access to - it's helpful to know. Running around on the day trying to get passes is a waste of time!
GEAR: Your gear is only good to you if it's functional so clean it all and check that everything you plan on taking is packed. For that matter, pack your cleaning stuff in a clean dry compartment - even if that means a Ziploc bag or Tupperware. It's definitely not a bad idea to get a filter for your lens(es) because sweat, booze and blood are not indifferent to the front of your lens.
MEMORY: Have you formatted your memory cards? Have you made sure that they're all working? Have you checked for errors? If you've bought Lexar storage then you have access to the Lexar Image Rescue Software. The software not only recovers photo and video files from any brand or type of memory card but also offers card reformatting and secure deletion features (so they're good as new), using any card reader and works with Mac or PC.
BATTERIES: When it comes to batteries; make sure that they're charged and/or that you have spare. Shooting all day and night will definitely deplete your little energy cells. Thankfully, if you're accredited, you may have access to the media area. This area is refuge for the weary - a (somewhat) safe place that you have to catch your breath, brush the dust off, recharge, dump cards, message your mom, and clean the DNA off your lens(es)... Otherwise you'd better make friends with someone in the area of the stage and hustle access to a multiplug.
LENS(ES): Which lens(es) do you take with? Well, which lenses do you have? Wide is good. Telephoto is rad. What kind of shot are you chasing? My advice is to pack the widest range then you've got the widest spectrum covered. Sometimes the stage is tall and deep while the pit is shallow - which means you can't see the performers as nicely as you might like to - in that case a zoom lens would probably be the best bet.
FIRST THREE NO FLASH: The, "first three", rule is as old as event photography itself - it stipulates that you shoot only the first three songs of a performance without flash. It's the rule for almost all festivals nowadays. I'm not sure where the rule originated. Could have been management. Could have been an artist. Could have been a venue or promoter. I'm sure that, for the most part, it is in place to ensure that the artists look their best. Flash photography can be quite disorienting for everyone so it stands to reason that the pit can't be full of strobes firing off erratically (besides the light show should be reserved for the stage).
DISCLAIMER: I had the opportunity to shoot with a speedlight/flash gun during the Crystal Castles set at Synergy Live 2015 thanks to their management. All media were positioned on the stage as well - it happens but not often.
WHAT ELSE: It's usually a good idea to pack a hat or some kind of shade device and/or sunscreen if you're heading to a daytime shindig. You can't go wrong with a hoodie, long sleeve top and/or rain-jacket for when the sun dips and the ghouls come out. My most important item is a pair of comfortable shoes because you're going to be on your feet all day and moving a lot - even if it's just in the pit. I don't think you'd do yourself an injustice by taking a water bottle with but checking what's on the festival blacklist will be a good indicator of whether or not you can stuff it into your bag. Earplugs are on a par with comfortable shoes because tinnitus is not a joke.
PRO TIP: The international rule is that after you have shot the first three songs you will be required to lock your camera away (no sneaky crowd shots of the stage) if you wish to stay for the rest of the performance. The alternative is that you take your gear and leave the venue. This isn't local organizers being quirky - it's an international standard.
Anything you want to ask?