Throw caution to the wind, if your not sure of the carb value of your Christmas meal then have a reduced insulin dose and correct later if necessary, this way you won't spoil your meal by going hypo (especially if you are dinning out) and can rectify your bg levels later.
If you want to eat a carb free breakfast go for it, you should also be able to miss it altogether and enjoy your lunch all the more if your basal dose is set correctly, if you do this just monitor your bg levels throughout the morning.