I agree you should keep the car stock until you know you will be going to the track often enough to justify proper track mods (10+ a year or more). If you've made that decision, then the basic items to get would be:
-Racing Brake Fluid
*ATE Super Blue works for me. You won't need it first couple times out, but once speed start to increase, better safe than sorry
-Racing Brake Pads
*Performance Friction 08s - Endurance Compound
*Don't screw around with stock pads at the track, they will turn into dust quickly at your level since you'll be using them often. Yes, it's true, instructors drive on them, but don't be fooled you can too without some level of consequence / risk.
*Negative camber will save your tires from wearing too quickly and help you a tad on the turns. Might be optional at the novice level though
-18 inch Track Wheels and Tires
*Keeps you from changing out costly 19 inch tires regularly. Also, R-comps come more readily in these sizes. 18x10 APEX EC7 Rims and NT-01 Tires should work well.
*Keeps the car from getting dinged too much from track debris or if you don't care it's optional. You could also just use painter's tape, but it gets old putting that crap on every time.
*Check out Harbor Freight Tools. Get a jack, impact fun, torque wrench, etc. so you can check your own car out and rotate tires for even wear. I guess you could just borrow this stuff on the track, but if you have the means to get it yourself - it's worth it.
*Supercharger is unnecessary and only will aid in burning up consumables (pads, tires, etc.) at a much quicker rate, even if you're a great driver. You're simply going faster and it takes more to slow you down or take turns. Also, it's another thing that gets heat soaked or can simply go wrong at the track - more hassle. I can't tell you how many serpetine belts I've helped change for my supercharger buddies...
*Suspension - coilovers would be ideal and will be a great add-on later. The truth is the stock M3 suspension is very capable. If you're serious about the track, try to avoid springs or a sleeve kit. They aren't horrible, but if you're going through the motions of a suspension upgrade, do it right the first time and get coils.
Good luck at the track and get yourself some track insurance. You may be a good driver, but others not so much
If you need any more advice before going to the track, feel free to PM.