Different states have different laws as to the percentage of alcohol needed to be in a container for one to be legally charged and convicted of an open container of alcohol in public. As a general rule, if a minor can legally be allowed to purchase a container from a store containing liquid with small traces of alcohol within it, that container is allowed to be open in public.In your situation, the one shot of vodka with the lemonade is more than enough alcohol in an open container in public to be charged and convicted of the crime that you are writing about.