Disclaimer - I haven't read any of this thread because I assume that it is mostly cluttered with useless bullshit. I'm gonna lay it down for you. What you do with it is all on you from there. Take it or leave it. IDGAF Fortunately, I happen to be bored and remember what it was like to be in your shoes, so I'm going to do you the favor of sharing what I've learned over the past 18ish years of playing with the devil's lettuce and other fun toys. Since you primarily seem to be concerned with the sweet, sweet, cheeba, and the occasional beverage, that's all I'm going to address at this point. If you decide that you'd like to add to your list, then we can address that in a later post. So, that being said, let's get down to business. (Please note that I'm posting this information under the assumption that you'll be given a whiz quiz as opposed to a blood or hair follicle test.)
First things first, what is your height, weight, body fat %, bone structure, etc.? Basically, what the fuck do you look like?
Do you exercise a lot? And I don't mean bullshit activity, I'm talking ball busting physical activity. The kind that leaves you huffing and puffing, and completely drenched in sweat.
How many ounces of water do you consume in a day? Not soda, not milk, not juice....water.
Also, what is your diet like? Do you eat a lot of fatty foods, i.e. fast food, fried foods, cheeses, peanut butter, 2% or whole milk, etc.? How many calories do you consume in a day?
The reason that I'm asking is because all of these factors ultimately affect your metabolism, which is going to play a huge role in how quickly toxins are eliminated from your body. The active ingredient in your shrubbery, i.e. the fun stuff, is stored in fat cells.
If you're a skinny dude, with the metabolism of a crack head (like me), you're going to be at a huge advantage vs. someone with 25+% body mass index (bmi) because you don't have as much fat for this stuff to hang out in.
If you exercise rigorously on a fairly regular basis, then you're body is going to naturally process these toxins much quicker than a couch potato as you'll likely have a higher metabolism
Drinking a lot of water regularly is going to help you stay cleaned out as well, not to mention the overall health benefits of being adequately hydrated.
Eating a lot of fatty foods increases the amount of time it takes to clear this particular toxin from your system.
Assuming that you are a skinny dude (like 90% of skiers), and you take the aforementioned items in to consideration, then you should clean out pretty quickly based on your stated consumption of "once every two or three weeks". I've popped clean 5 days after a night of fun on multiple occasions without any other detox "tricks" other than what I mentioned above. {To give you a reference as to my size, I'm 5'9", 155, and about an 8% bmi. Not to sound conceited, or like a douche bag, but think David Beckham but a few inches shorter. (Still comes out douche-ish, but you get the idea.) I exercise 6 days a week, sweat like a whore in church, drink about 150+ oz. of water a day, and consume between 5,000 - 6,000 calories a day.}
Now please note that everyone's body is different, so I make no guarantees that what works for me will 100% work for you, but you get the general idea. The generally accepted 30 day cleansing period is more applicable to a daily smoker vs. someone who only partakes bi-monthly. If most of the above applies to you, you should be clean in a few weeks TOPS. You'd have to have pretty shitty luck if they pop you a day or two after you blow.
If none of the above applies to you, and you're a fat, unhealthy, bastard, then all hope is not completely lost. There is an amazing device that is pretty readily available on the interwebz called a whizinator. (I'm sure there are other names for them, too, but that's what I've always heard them called.) Basically, all it is is a small bag with a small tube. The bag has a heating pad attached to it that is powered by a 9 volt battery. It also has a thermometer so you can make sure your piss is the correct temp. Once acquired, all you have to do is get clean, piss in a sterile container that you can use to transfer to the bag, and keep it ready to go at all times. You drop that shit in your crotch and empty the clean piss for your test. Guaranteed pass as long as you aren't a gomer and get caught with it. Dude would literally have to be holding your dick for you though for this to happen, or you'd have to be completely retarded. If either applies, you've got bigger problems in life.
As to the alcohol, if they're giving breathalysers, then you'll definitely be fine come Monday as long as you don't get hammered on Sunday (or a weeknight). Even if they give you a blood test, you should be fine within a couple of days. Alcohol metabolizes pretty damn fast, so I wouldn't really sweat it as long as you aren't a raging alcoholic that drinks several times a week. If you limit it to Friday and Saturday nights, then you should be clean come school time. This link does a pretty good job of explaining alcohol metabolism.
http://pubs.niaaa.nih.gov/publications/aa35.htm
I should also note that I am skeptical of their claimed testing. Testing for all of those substances is INCREDIBLY expensive, so I'm guessing that it's more of a scare tactic than it is the reality of the situation. It is not financially feasibly for them to test every "random" student for ALL of those substances. (Unless you happen to go to harvard or something.) Steroid tests are not cheap. Unless they have a reason to suspect it's use, then I call bullshit on them testing ALL of those substances. It's probably your standard lab test that tests for thc, cocaine, opiates, benzos, and amphetamines.
OK, I've rambled enough. I hope it all makes sense. Good luck dude.