I have been.
Best to first read thru some reviews. John Farnam goes every year and writes a review every year. You can look back through his website Defense-training.com in the "quips quotes and lessons learned section. Look for the date around 1st week of June every year and you'll find his reviews of like the last 10 NTIs.
You can also check out my review of the one in 2007. It is posted at NTI 2007 REVIEW - Tennessee Gun Owners among other places.
What to bring?
Seriously. It is not a "hardware" intensive experience. It is a "software" intensive experience. In fact if you want to you can avoid fights by using your awareness, verbal skills, and feet. Or if you want to you can get into gunfights. In fact that is one of the quotes I heard. "If folks come here looking to get into a gunfight...they probably will. If they come here looking to avoid a gunfight...they probably will."
Now, I have heard of people emptying 3 guns in a shooting scenario. They must be missing...A LOT. I do not think I ever even drew my backup gun.Shoot accurately. The knock down targets have to be knocked down. So again...shoot accurately.
One piece of "anatomy advice"....the knockdown manequin targets have a 3" diameter gravel filled PVC pipe "spine".If you hit it they fall over. If you don't then they may not fall over. It only goes up to chin level. Head shots with pistols or rifles zip right thru the head and will not drop them. I know from experience.
Of course they do not expect people to shoot targets in the head so they figure that anatomical anomoly does not matter. I shot some targets in the head on a stage where we used "battlefield pickup" shotgun in a CQB environment and they went down. Of course the guy running that stage was highly disturbed by the idea of head shooting people with a shotgun. But on another stage I emptied a pistol into the eyesocket of a target at about 6 yards and it did not fall over. They had to "declare it dead". So Don't shoot for the head and expect to get realistic results.
On the FOF stages just act natural.If you are nice to the role players and cautiously friendly and pay attention to body language you'll do fine. If you are a jackass to the role players they'll either fight you or rob you or not help you when you need help. If things look odd or out of place extricate yourself from the situation . Common sense.
Hope that helps some.