Students generally feel that they can get away with a reasonable amount on campus, and that's pretty accurate. A lot of it can depend on your RA or RD, who will be the person writing you and your neighbors up and who will be the ones reporting you. As far as alcohol goes, if you keep things fairly calm and aren't blatantly causing a ruckus, you shouldn't have a problem. Drugs are taken more seriously, and use of them in the dorms isn't usually a good idea-especially marijuana or other drugs that have an easily identifiable odor.
Punishments for getting caught usually aren't too bad; most include a "rehabilitation program," where you go to a drug/alcohol awareness seminar for an afternoon. Repeated offenses can add up though, and eventually the punishments will get serious.