Looking through my repertoire list (also known as all the songs I've forgotten) the only song I wouldn't sing in a folk club (or anywhere else) is "The Engineer". Nowadays I usually sing "Where have all the Flowers Gone" in German, especially if there any native German speakers in the audience, and the last time I did in English I found I was back translating. As for the Fields of King's Ford, it's a fantastic song to sing at Croke Park with 80,000 Irishmen (just as part of the crowd), though I'll usually sing it if anybody's sung "Caledonia".