Contra dances I have attended use a variety of music from the English, Irish, and American dance and song traditions. In every case I can remember, the band strung several melodies together, just so they were all 4/4 or whatever, and compatible with the choreography. So if the band started, say, with "The Rakes of Mallow", it would after a few cycles of the choreography switch to some other tune in the same time signature.

T.