Perhaps you can lay a little groundwork first? Actually, perhaps you can get THEM to lay their own groundwork, by asking them why THEY keep relics, and for what purpose?
I’m sure you will get a few blank looks. But ask them again: “Why do YOU keep relics?”
Then you could ask them if any of them have ever gone to a concert, play, sports event and still have the ticket. Or does anyone have a treasured photograph? Or does anyone have a seashell from a particular beach?
Obviously there will be many examples of “relic-type” things, and many natural and very human reasons for keeping them. And maybe with this foundation you can transition into Relics proper and the theology behind it. Grace builds on nature, right? So then you distinguish betweeen these natural relics and Relics proper, and how God gives grace associated with certain material items as they raise our minds and hearts to God.
What do you think?