You could use Christmas cookies!
Little cupcakes with blue or pink inside. Even green for boy and red for girl..switch it up! Lol ;)
I saw on pinterest where they asked the doctor to put gender in envelope and you go pick out a boy and girl outfit. You have the cashier look and then gift wrap the outfit and open it up in front of every body!
Put pink or blue bows all on the Christmas tree while everyone's asleep.