I avoided the Christmas parties because they included the husbands, wives or SOs of the people I worked with. A lunch, though, I would take part in and assist with because it was only for the people I already worked with and knew. If there are a couple of people there that you are comfortable with then just sit at their table and enjoy the food and friendship. It might be a good way to start getting used to socializing but only if you think you can be fairly comfortable.