Bouquet of Roses
Crazy Arms
Candy Kisses
Rolling Home (Tams)
Old Brown's Daughter
Row On
Constant Lovers
Waltz Across Texas
Wishful Thinking
Paper Moon
Crazy
Road to Mandalay (Peter Bellamy tune)

More than 10. All these songs have the features that either they can be sung walking to the subway, can be sung at a bluegrass/country session, have good choruses people can join in with easily--or a combination of the above.

Except Road to Mandalay, which I just think captures the flavor of its time perfectly. And besides the Bellamy tune is great for climbing hills.