Full fig. Full dress. A corruption of the Italian in fiocchi (in gala costume). It was derived from the tassels with which horses were ornamented in state processions. Thus we read in Miss Knight's Autobiography, “The Pope's throne was set out for mass, and the whole building was in perfect fiocchi” (in full fig). Another etymology has been suggested by a correspondent in Notes and Queries, that it is taken from the word full fig. (figure) in fashion books.
“The Speaker sits at one end all in full fig, with a clerk at the table below.” —Trollope: West Indies, chap. ix. p. 101.
or Figo. I don't care a fig for you; not worth a fig. Anything at all. Here fig is fico—a fillip or snap of the fingers. Thus we say, “I don't care that for you,” snapping the fingers at the same time. (Italian, far le fiche, to snap the fingers; French, faire la figue; German, diefeigen weisen; Dutch, de vyghe setten, etc.) (See Fico.)
“A fig for Peter.”
“The figo for thy friendship.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894