Garage pass IS a must, in my opinion. Seeing how efficiently they can reassemble a busted up car is awesome to watch in real time. And youre RIGHT THERE, it's a cool experience.
I like watching the first 45 minutes or so from the grandstands just beyond turn 1 - usually some action going into turn one the first few laps, and you can see all of the infield bits from there (everything, really).
For me, I'll watch till about 11, go nap in the car, up at 1ish to walk around, back in around 230 or something and another 90 minutes of napping. Rinse and repeat until about 8am then Im up and watching all the action.
Move around, get different angles. If taking a DSLR - bring lots of cards or a computer to get rid of pics. I usually shoot about 3500 at a 24 Hour of Daytona, and shoot as high of resolution as possible.
Weather: it'll be so lovely (typically, when sun is out!) during the days, but it'll get chilly at night, so bring a jacket or hoodie. And beanie.
A backpack is nice for when youre walking around, lot of free stuff given out, shirts and stuff. Maybe you stop by the GRM tent and buy a shirt/subscription ...not fun to have to carry those things.
At night, I love going to the international horseshoe and seeing those brakes glow orange.
Ive camped before and enjoyed it. Ive also had experiences where I leave for a while for dinner, which is a nice 'break' from the noise and a good meal. I usually hit up Outback across the street, they'll the race on and you never know who you'll be seated beside of at the bar. One year the first guy was the brother of Michael Shank, if I remember right. Then, taking his place, was the father of one of the drivers for Red Dragon when they were running a DP (this was maybe 2010 or so, it's been a while, I forget the year). It was cool, just chat, enjoy a steak, watch racing.
HAVE FUN. Let us know how it all goes. I want to be there this year, but I think I'll have to wait till 2023, got a wedding to plan and pay for, so cutting out a few things here and there.