If a rowdy bunch, maybe "Irish Blessing" to mellow things a bit. If moderate energy or a laid back bunch, lately we close with "We Are Family" and we get the audience clapping. Most of our audiences tend to be of the latter two types because we do mainly retirement residence gigs. I think the lyrics in general and the reference in "We Are Family" to "...all my sisters..." works well for us on several levels:
~we're an all-women quartet;
~we have mostly female audiences, at least 10:1 in our RR gigs (both due to death rates by gender and, pardon the stereotyping, often the hockey/ball game starts at the same time as we do).
~our audiences have told us they identify with us: we remind them of their past singing days, very often with other women or family;
~our style uses constant eye contact with audience members while conveying the emotions behind the storylines of the songs, which creates a depth of contact that our audiences may miss sharing with their own family or close friends, so the words match our behaviour.

Geez, after articulating all this at once, it reinforces why we enjoy this type of gig so much.