A.H.
Hmm... as someone that tries hard to see things from all sides; aside from the economy and the tightness of finances, is there a reason you feel you cannot participate? Perhaps the office feels that if you participate, it may help you feel better about the holiday in general and raise your spirits for everyone included (such as your family and yourself)? I am not sure they are trying to be selfish. I hope that if you are 'walking out' is is on the meeting and not your job as that is a bit more dramatic than what they are trying to provide. It sounds as if you are in a fun place to work (and I only work from my home).
Last year, I could not get into the spirit of the holiday, barely put out the decorations, and I was guilt-ridden as I have a small child that thankfully does not remember! This year, I am determined not to be that way, even if the money is not there. You can still have a holiday without the money. And you can tell that to your boss/ manager. Communication is always key in life.
You are in charge of your life, but I honestly do not see any harm in celebrating and having a little fun with everyone to raise your spirits. You may be against it now, as it was a awful last year, but you may also be surprised and it is the disasters we sometimes fondly remember and laugh about, and that is always the best medicine.