Having read through this thread, and because this is the internet, I feel compelled to offer my unsolicited $0.02...
I've attended almost a dozen of Barney's clinics and matches since the very first one back at Yankee Range. The overarching piece of advice I could offer to the first-timers is
RUN WHAT YOU BRUNG!!!!
This is all about learning (and a helluva learning experience it is!). If all you have is a single shot hunting rifle, Norinco ammo, and the cheapest scope out there....bring it and shoot it! These clinics are designed to introduce you to PR (and PRS) matches and all the gear that that entails. You will meet a tonne of shooters with a wide range of experience and equipment that you can pick their brains, look through their optics, handle their rifles, dry fire their triggers, test their rear bags, etc...
Use the weekend to figure out the shortcomings in your setup, and decide what upgrades you need to make before the next match. There's no need to show up to the first clinic with the 100% solution (although the gun industry and Visa would be happy to help you out with that...ask Dr. Schmidt & Dr. Bender!).
A few specific points:
Ballistic Calculators: Grab an app or two and plug in your data and see what it spits out for solutions. Make sure you're diligent in your inputs because Garbage In = Garbage Out. All calculators should be identical within the 600m shot during the clinic. Also, since you're doing a walkback, you'll get actual "did hit" data vice the calculator's "should hit" data. Compare the results and see if they agree with each other. With the exception of Applied Ballistics (and their CDMs), most other calculators will give you the data to get on paper.
Kestrels: A nice to have, and will help you derive the Density Altitude (or atmospherics) for use in your calculator. The wind (at the shooter) will give you an initial wind call, but will require you to factor different winds throughout the flight of the bullet. At 600m on the ranges we shoot on, i've never used more than .1-.2mils of wind. There will be enough Kestrels out there to give everyone a good baseline to run their ballistic apps.
Bullets: Again, run what you've got. At 600m, 168gr bullets will do just fine. If you're building a load for longer than that, then there are better bullet choices and frankly, better calibers suited to that application. If you're doing load development before the clinic, run a ladder test or OCW and determine the nodes in your system to get the best load possible. Consistency is key.
If you want to show up with the 100% solution, head over to the "What the Pros Use" on the Precision Rifle Blog, and open up your wallet. The PR game relies on a tonne of support gear in addition to a consistent rifle, ammo, and shooter. Beyond a capable rifle and consistent ammo, bring your rice filled sock/rear bag, your coin-operated scope, and your internal 4rd box mag, and put some lead downrange! You'll quickly figure out where your money is best spent on buying the right gear for you, and there will be a bunch of great guys out there willing to answer all your questions.
Over time, your setup will evolve and tailor itself to your needs...I know my gear has been improved upon over the last 4-5yrs, and I'm still not at the final solution. Enjoy the clinic, and I hope to see you guys there!