What follows is less about how many stacks of such and such reagent you should bring, and more about controlling the irrational pressure that the gaming community puts on new people. Most of what you read from the hardcore and most of what you hear from the vocal people you encounter in-game gives the appearance that on day one, you're supposed to know everything, be skilled at everything, and be immune to human emotions.
I say BUNK. A person's first raid can be fun, exciting, and also nerve-wracking. To keep the night focused on the fun/excitement and less on the painful side, here's some food for thought.....
Before the Raid Night
1) You are New, but you are not a noob - The word "noob" comes with such negative connotation in WoW. Forget that crap. But you are new, so accept that (A) you might make mistakes, (B) its totally ok when you do, and (C) someone might call you noob when you do. Ignore them when they say that. Just wait. They'll mess up soon enough, and you can do a Victory Dance in your house when they do :-)
2) Prepare ahead of time - Polish your gear (gems enchants etc), stock up on elixirs and potions and food. You know your raid is friday or saturday? Get your stuff squared away on wednesday or thursday. Make sure your Vent is setup in advance.
3) Scouting - This might sound funny, but your first time in, you might not know where the instance is located. In Conquest's first 25-person raid, I didn't know where Obsidian Sanctum or Naxxramas were, other than what's listed on Wiki, which is "dragonblight". Dragonblight is a big place, and knowing the exact locations beforehand will make you feel less like a noob come raid night.
4) Don't worry about Boss Fights - Here's a place where I diverge from the popular concept of knowing boss fights in advance. If your raid is planning on tackling a large chunk of Naxx in one night, you will be way way way too confused if you try to research each boss. If you're planning on doing only one wing, then definitely read up and try to watch some vids. But 14 bosses is too much to digest. Ask questions if you're unsure of how a boss works.
At the Start of the Raid
5) Be Early - if possible, log in an hour early on the night of the raid, with plans to do nothing but think about the raid. You'll probably be excited and nervous, and allowing as much time as possible will help reduce anxiety. And since you already scouted out where the place is, you'll have plenty of time to get there and help the other early guy summon people.
6) Repair and get Ammo - I don't care what consumables or mats or whatever else you pack. If you only do two things before the raid (A) Repair and (B) Full quiver. Oh, and remember to bring your DPS pet.
7) Growl off, Passive stance - I know, I know. But its at these exciting moments of a first raid that we forget the basics. Growl off, passive stance.
8) Know Your Tanks - Make sure you know who the tanks are. It works somewhat better to Misdirect onto them than onto the other players.
9) Know Your Targeting - For target selection, you should either have a designated Main Assist, a raid icon kill order, or at the very least, a tank who you will use for selecting your next target. Ask about MA or Kill Order at the beginning, and if there's no satisfactory answer, just pick a tank and assist him/her all night.
During the Raid
10) Fire Bad! - Generally, anything funny looking on the floor or flying down from above is bad. Step out of it.
11) Ignore Recount - Whether you run a damage meter yourself or not, I'm sure some idiot is going to post a recount report to /raid at some point in the night. Completely ignore the output of the report, unless you're on top :-P and also completely ignore that person going forward. It is hugely detrimental to team unity when those people spit out those reports. Definitely review WWS after the night is over for constructive feedback, but for now, ignore it.
12) Turn off Viper - Once your mana is full, turn off Viper. Uggy, I hate when I do that.
13) Loot your Badges - ...er...Emblems. Dead boss means (A) Phat Lewts, and (B) Emblems of Something. Don't forget to loot your badges.
After the Raid
14) Sleep. Or Not - If you're like me, you spend the hour after a raid totally wired. The first few raids I was in, it was like two hours before I could even consider falling alseep. It is exciting stuff. But that's just me. Maybe you'll sleep like a baby.
15) Empty Your Bags - I have maybe 15 bag slots filled with raid stuff. I hate when I forget to empty my bags and then head straight out to quest or gather, and suddenly find my bags full. Empty that raid stuff out into your bank.
16) Review WWS - depending upon when the report gets posted, maybe you view it that night, or maybe the next day. Take a look at things like how many misses, or what percent of your DPS came from what abilities.
17) Growl on, Stance of your choice - I always forget to turn growl back on, and then the next day I wonder why the first mobs I solo run right up to me. Noob!
So there you have it!
Some might be obvious, some might be all emo and carebare and touchy-feely. Some of these are things I do at the start of each and every raid, whether its a farming run through Kara at 70, or a 3 Drake progression night at 80.
Its all about keeping calm and remembering the basics.
Fire hurts. Mobs hit the thing with the highest threat. Empty quivers fire no shots.
I can't wait to hear about how it goes.