Psiguyy said:If it's a kosher event, absolutely avoid milk, beef, and pork. Safer to stick with precooked fish and chicken for the meats.
As for precooked add-ins, that's up to you. Depending on the ingredient, I like to precook some and stick with raw for others. For instance, I prefer cooked mushrooms to raw.
In some kosher circles, chicken is considered meat and cannot be used with milk. Fish, especially smoked salmon or lox is the good choice.