Green’s Dictionary of Slang

any nameless small object, typically some form of gadget .

1905		J.W. Carr ‘Words from Northwest Arkansas’ in DN III:i 77: do-funny, n. Strange object. ‘Look at that do-funny over there.’.
1905		L. Pound ‘Dialect Speech in Nebraska’ in DN III:i 66: Indefinite expression applied to something, the name of which is not readily recalled [...] doo-funny, doojum-funny.
1914		J.C. Ruppenthal ‘A Word-List From Kansas’ in DN IV:ii 105: dofunny, n. Any small article. Also dufunny.
1918		Electrical Experimenter (NY) Aug. 272/2: ‘What do you call these do-funnies?’ our young officer asked of him, pointing at the mysterious objects.
1922		P.A. Rollins Cowboy 153: Each of such useless objects [...] particularly if it were small in size or novel in construction, was apt to be called a ‘dofunny’.
c.1943		‘Bill O. Lading’ You Chirped a Chinful!! n.p.: Do Funny: In lieu of technical name. Also Gismo.