Topics for on-site interview lunch and dinner time

Actually, this advice is quite different from that of Wetenschaap, though I don't disagree with that suggestion.

Instead of talking about yourself, spend the time asking about them. Ask about the students. How motivated are they? Ask whether there are unique aspects of the educational program. Ask about their future goals. Ask about trends, both positive and disturbing that they see on the horizon. Ask about collaboration. Ask about the research of others. Ask about what research seminars are available.

And these are things you want to know before accepting an offer.

Or ask about the local environment. Are there good places to, say, ride a bike or hike. If you have a partner, ask about opportunities for them locally.

Lots of things. But don't make it too focused on yourself or you might seem narcissistic.