Without wanting to appear to be the Christmas humbug, some quick tips and pointers for management.
Events being off-site or after hours does neither admonish the Employer's responsibility from duty of care for their staff, nor exempt workers from the company's code of conduct.
If you expect trouble it may be worth highlighting the fact that drinking to excess, antisocial behavior, use of illegal drugs, fighting, the use of bad language, inappropriate sexual conduct, and so on, will be considered to be acts of serious misconduct. Ensure you have polices on Drugs & Alcohol, Bullying & Harassment and Disciplinary Procedures.
Management want to be seen as generous, but don't supply limitless free alcohol, and always provide food. Management staff need to set the tone for behavior and conduct, and it's recommended to have an official end to the festivities. Name a time and stick to it. If you know a worker is intoxicated assist in a plan to get them home safely.
If your party is off site be diligent and ensure the venue provider is across their Health & Safety obligations. Will you be exposing your workers to any risks you and your staff need to be aware of? If unsure ask the venue staff and document any diligence with a paper-trail.
All being well the xmas party is a great opportunity for all staff to bond and relax away from the pressures of work.