For those looking for an easy way to introduce the proper texts, try singing this versification of the Gaudeamus to any Long Meter tune as the bell signals the beginning of your opening procession.
If followed by the oft-sung For All the Saints, there’s rather a nice textual segue.
Today let our joy be increased
In celebration of the feast.
For all the saints, the angels raise
To God the Son glad songs of praise.
Update: As a reminder, the 2015 Advent Calendar of Hymn Tune Introits may be found here.