I was on my way home just a few days ago, taking a short-cut through Trinity Belwoods on a sunny afternoon, and saw a couple, presumably on a date, being ticketed by cops for possessing alcohol. What a bummer.
Regarding pissing and puking in the park while intoxicated, there's really nothing stopping an individual whose had one too many at a nearby bar to do either of those things in the park while drunkenly stumbling on their way home. It's not as though the place of alcohol consumption necessarily dictates where the consequences of said consumption will play out, and even then, why not target those specific activities instead of the park itself?
I really don't get why do our laws have to be so black and white. Why not have specific laws, singling out harmful activities? Such as violence. Or pissing. Or puking. Or littering. Or being belligerently drunk. Or massive, loud gatherings at 1 am. Those are not ambiguous terms that would be difficult to legally define and that would otherwise be difficult to charge perpetrators with were it not for the umbrella by-laws prohibiting drinking in public spaces.