Couldn't you just fill the beverage in a non see through water bottle? I have one of these insulated metal bottles where no one would notice what's in there.
I guess the biggest problem probably is to "not make a scene" cause here in Germany we young people typically have many public spots where people drink lots of alcohol, listen to loud music and party. These aren't restricted places, those are just public spots of cities where many young people gather and typically party through the night (like on grass fields at a river or lake).
Idk how strict America is in that regard cause the media often portrays it as if there are lots of harsh police officers because people are allowed to carry guns and are more violent/unpredictable.
In Germany at least where I'm from you rarely see any police officers and if you ever see some (maybe twice a year when there's a car accident) they were just normal introverted people. One time I was very drunk when I was 17 or so and I talked to the police and they were just chill. I guess the typical Germans are more nerdy type people and the worst they could get is to argue about a math problem but I never see them get physical.