* Water, in a clear bottle, no label, unopened.
* Pencil case on the floor at all times.
I'm not sure if it's an official rule or not but I know for my senior years at school (years 11-12) it was a rule for all our exams. You might and probably would. No, I never took anything into an exam except exam equipment - once I sat down I didn't get up until I finished.
By yearlies I assume you mean trials or if you talking about your exams at the moment then you would mean half yearlies. Your trials are most probably worth a considerable amount to your assessment (i.e. sometimes up to 30%) while your half yearlies are probably worth 10% or so. Either way it's not really worth risking it just because you think your teachers "don't have the balls". Given that it isn't up to your teachers since usually exams are supervised by external supervisors to the school - they don't know you, they don't really care and they will adhere to their rules and guidelines and that could mean failing you. Although at most I think they would just take your drink from you if anything.
As for alcoholic drinks, I've heard/read stories on here about people turning up hungover to HSC exams.