A milk-free margarine can be substituted for the butter. In moderation, these should not change the taste significantly. The same advice works for gravies as well. Stock, water, or a milk substitute of any of the kinds mentioned above should produce a thick, rich gravy. I know all families have their own specialties at the holiday table, so just use the same general advice and work out substitutions.
Desserts are tough.
Although some substitutes work just fine in recipes, unless you re a good cook, it can be hard to make the daintier and more delicate delights come out right. Again, a kosher bakery can help. The one closest to me even makes a completely milk-free pumpkin pie that tastes great. Eating out in restaurants is a little safer than it used to be. The better the restaurant, the more likely they are to work with you to create milk-free foods.