Eating Christmas Food in Islam
Question

What is the ruling on eating food prepared for a Christian festival? What is the ruling on accepting their invitation to their celebrations of the birth of the Messiah (peace be upon him) [i.e., Christmas celebrations]?
Praise be to Allah.Is it permissible to celebrate innovated festivals?
It is not permissible to celebrate innovated festivals such as the Christmas of the Christians, or Nowruz (Persian New Year) or Mahrajan (Persian festival), or festivals that have been innovated by Muslims such as the Prophet’s birthday in Rabi` Al-Awwal or the Isra’ in Rajab and so on. 
Can a Muslim eat Christmas food?
It is not permissible to eat from that food which the Christians or non-Muslims prepare on the occasion of their festivals. It is also not permissible to accept their invitations to join them in their celebrations of those festivals, because this encourages them and is tantamount to approving of their Bid`ah, which gives the wrong idea to ignorant people and makes them think that there is nothing wrong with that.
And Allah knows best.