Yes, you can absolutely begin drinking on embarkation day as soon as you step on board the ship. In fact, for many cruisers, "Embarkation Day" is synonymous with "Sail Away" celebrations, and bars in the main atrium and on the pool deck usually open long before the ship even leaves the port. If you have purchased a beverage package, it typically becomes active the moment your key card is scanned at the first bar, though some state and local port taxes may apply to drinks served while the ship is still docked in certain jurisdictions like Texas or New York. One thing to be aware of is that many cruise lines have a "safety first" policy during the mandatory Muster Drill; bars will briefly close and service will be suspended while the safety briefing takes place to ensure all passengers are attentive. Once the drill is completed and the ship prepares to depart, the bars reopen, and the party continues. It is a great time to explore the ship’s various lounges and find your favorite bartender for the rest of the week.