Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

 

We are allowed to eat foods prepared by Christians as long as the foods are lawful for us: in other words, we are not allowed to eat pork or its by-products, or foods cooked in wine, etc.

We  may eat the meat they have slaughtered by their own hands.

 

The fact that foods are served during their celebrations or feasts in themselves do not make them unlawful. That will be the case if they immolate them to idols. That does not apply to Christians or Jews; it only applies to those who practice idolatry.

 

Almighty Allah knows best.