A minor can legally drive with alcohol in the trunk or car as long as they are accompanied by someone of legal age to drink.
If the minor is driving with someone 21 years of age or older and the person 21 years or older wants to transport alcohol in the car then they can do so.
The minor must be accompanied by an adult 21 years of age or older to legally transport alcohol.
For example if you're a minor and you drive a friend that is 21 years or older or your brother to the store to get alcohol then you can legally transport that alcohol.
However if you're not driving someone 21 years or older with you then you cannot legally transport alcohol even in the trunk.
However if the alcohol is in the trunk then it's out of sight and likely you'll not get into trouble because police have to have probable cause to search the trunk or car or have a warrant.
You must be 21 years old or older to drive a vehicle with alcohol in it.
To transport alcohol in a car or other vehicle legally you must be 21 years of age or older.
Since you have to be 21 years old or older to purchase and possess alcohol it's the same with the age you have to be to transport alcohol.
However if the alcohol was in the trunk of the car or in a locked tool box then you could get away with transporting the alcohol when under 21 years of age.
That is as long as you're not drinking it and have no alcohol on your breath.
The police would need your consent to search the toolbox or trunk without a warrant.
So if you need to transport alcohol when under 21 years of age make sure it's sealed and in a trunk or toolbox that is not seen.