Green’s Dictionary of Slang

1. a poor (Southern) peasant.

1889		Western Kansas World 19 Oct. 1/6: I’m simply an old ruta-baga from the agricultural deestricts.
1900		H. Garland Eagle’s Heart 84: ‘Any objection?’ ‘You bet we have, you ruta-baga. You better keep out o’ here.’.
1920		Ade Hand-made Fables 63: For every Pansy in this Conservative Town there were 14 Rutabagas. You Know — the Cracker and Milk Buddies who shave their own Necks.

2. an ugly woman.

1938		D. Runyon ‘Neat Strip’ in Runyon on Broadway (1954) 607: Any pancake may have the same specifications and still be a rutabaga.
1970		G. Greer Female Eunuch 266: Who likes to be called dry-goods, a potato, a tomato or a rutabaga?

3. (US) a dollar.

1951

S.J. Perelman cited in DAS (1975) 439/2: We’ve spent 60,000 rutabagas combing the country for their exact doubles.