Choose an eco-friendly venue: Look for a space that is known for its sustainable offerings and one that will make it easier to handle logistics in an eco-friendly way. Look for a venue near the office or that can be reached via mass transit.
Mind your decor: Avoid fresh flowers. Instead choose pine cones, acorns, pine boughs, greenery from the yard or reusable holiday decorations.
Do the dishes: Use washable dishes, glasses, flatware and linens that can be reused rather than discarded. Should it be necessary to go disposable, try to use products made from recycled and/or compostable material.
Give green gifts: A holiday party may include a little something for the attendees to take home. Good choices are organic or recycled gifts or gifts that benefit the environment. Useful items such as a pen, comb or seed packet are wise. Or, consider a photo booth where attendees can have a photo taken.
Alderton, Matt, http://www.successfulmeetings.com/Event-
Planning/How-To/How-to-Host-a-Sustainable-Holiday-Party