I recall reading that the cowboy most often sang without the benefit of any instrumental accompaniment. The guitar was associated with him more in the popular imagination than in reality - guitars were few and far between. The banjo was more familiar around cow camps, but not too familiar. The preferred instruments were the fiddle and the harmonica, particularly the latter which was easy to play and carry around. The concertina may well have been another - I don't know, but I am sure Sandy, Art, Joe and others will be able to fill you in.

--Stewie.