Hi Fleur,
I agree with some of the posts here that the New Year celebration might not be the occassion that people want to give up.
How about a variation on the basic idea. People returning to work in the new year will have over indulged over the Xmas and New Year break. Why not organise a lunchtime 'fast' a over the first couple of weeks?
I don't mean every day but perhaps one day a week. People could do without lunch, they could lose a little weight, they get to feel in just a small way what it is like to feel hungry and contribute their lunch money to the Red Cross or similar aid agency.
Eyeslice