That was a dead giveaway for me, too. I never turn down champagne!
Otherwise, you could have a present under the tree unlabeled that would be for a newborn baby (unless there will be a baby or another pregnant woman in attendance). Someone will have to open it to see what it is and who it's for.
ETA: Oops, I read through the thread too fast and see Miss Mousie suggested this too!
Also, congrats!