Hi Graham,
Even on secular gathering, i usually play few universal worship songs like How Great Thou Art, Amazing Grace, some contemporary praise songs like Seek Ye First, Glorify Thy Name, Israelites song like Hatikvoh, Hava Nagila, Shabath Shalom, Go Down Moses etc without offending anyone. I usually start the get-together by praising our Almighty Father in Heaven & thanking the host of the party.
Jimmy