I was once told that it was the custom in the old Synodical Conference for a Christians's confirmation verse to serve as the sermon text at his funeral. I have no idea what the history of this is (a German thing? a Medieval thing? a Lutheran thing?) and have only half heartedly tried to track it down - maybe one of you will know. But I have found it of immense practical use. A confirmation verse gives, as it were, a port of entry into the Gospel that must be preached at every Christian funeral and thus helps keep the preacher from falling into worn out clichés.
What to do when the church records do not give a confirmation verse (especially common with adult confirmations)? Look at the propers for the Sunday of the week in which the confirmation took place and choose a verse from those propers - the Introit, Gradual, and Verse are the richest mines in this regard.