Green’s Dictionary of Slang

1. (US) an out-of-the-way drinking saloon.

1859		Matsell Vocabulum 80: side-pocket A drinking-saloon in an out-of-the-way place; a resort for thieves.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1895		C. Crowe Aus. Sl. Dict. 74: Side Pocket, a resort for thieves.
1901		Argus (Melbourne) 20 Sept. 6/4: The haunt of such men is the padding-ken, a side pocket, a flash ken, or a flash panny.

2. used in a variety of phrs. implying a lack of need, e.g. as much need of a wife as a dog of a side-pocket, of a worn-out old man; want as much as a toad/dog wants a side-pocket, does not want/need at all; UK uses tend to use toad, US are more varied, e.g. hog, pig, sow.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: He has as much need of a wife as a dog of a side pocket; said of a weak old debilitated man. He wants it as much as a dog does a side pocket; a simile used for one who desires any thing by no means necessary [...] As much need of it as a toad of a side-pocket; said of a person who desires any thing for which he has no real occasion.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1833		Essex Herald 9 July 2/6: Livngs had no more need of a servant than a toad had need of a side-pocket.
1846		Bristol Mercury 14 Feb. 6/6: ‘You have as much use for a wife, I think, as a toad has for a side-pocket’.
1881		John o’Groat Jrnl (Caithness) 16 June 7/5: Speaking of a youth who had married imprudently, ‘Why, he didn’t want a wife any more ’n a toad wants a side-pocket!’.
1883		Wkly Nevada State Jrnl (Reno NV) 8 Sept. 2/6: These two offices (Recorder and Clerk) do no more need a deputy than a ‘pig needs a side pocket’.
1886		Pickens Co. Herald (Carrollton, AL) 30 June 1/3: We need a stock law here [...] just about as much as an old sow needs a side pocket to carry her extra corn in.
1891		Burlington Free Press (VT) 11 Apr. 7/2: I don’t need it any more than a cow needs a side pocket.
1893		Marion Star (OH) 26 Sept. 7/7: ‘It [i.e. chatter] isn’t needed any more than a toad needs a side pocket’.
1896		Times-Picayune (New Orleans, LA) 20 Sept. 24/1: ‘I don’t need this coat any more than a pig needs a side pocket’.
1900		Folkestone [...] and Cheriton Herald 27 Oct. 6/3: As far as the speaker was concerned, the town wants tramways about as much as a toad wants a side-pocket.
1907		Quorn Mercury (SA) 16 July 2/7: Cr Parker—So the work won’t be done. Cr Warren—It is no more needed than a toad needs a side pocket (laughter).
1907		Belle Plaine News (KS) 28 Mar. 2/2: Belle Plaine needs a second paper just as much as a toad needs a side pocket.
1909		Ulster Gaz. 7 Aug. 7/3: Two lads who [...] seem to have as little call for boots, stockings, or jacket as a toad has for a side-pocket.
1912		Alma Enterprise (KS) 9 Feb. 4/2: A farm advisor is needed about as bad as a hog needs a side pocket.
1914		Eve. Kansas-Republican (Newton, KS) 14 Feb. 2/1: Newton needs another newspaper about as badly as a toad needs a side pocket.
1923		Argus-Leader (Sioux Falls, SD) 29 Mar. 10/1: ‘I don’t need it [i.e. a shirt] no more ’n a toad needs a side pocket’.
1925		Diss Exp. 6 Nov. n.p.: A man as is said to need a wife, ‘as a dog needs a side-pocket’.
1989		Ft Lauderdale News (FL) 31 Aug. 8A/3: ‘We need it [i.e. a new law] like a toad needs a side pocket’.