It reduces temptation to snack on the job. Make sure one person is in management. Have a member of senior management take over book-keeping responsibilities for that time. Keep storage rooms locked. Give keys to specific individuals and hold each accountable.
Accountability is difficult in open-bar service.
Experiment using pourer spouts which premeasure shots. When it comes to in-house restaurant security, being small can have advantages. It's an amusement, not an issue. But in an industry where cash passes through many hands, human traffic is nonstop and food and drink is money, stealing is a fact of life. So are the unpleasant statistics.