Green’s Dictionary of Slang

1. a small amount of money, a reward or bribe.

c.1698		B.E. Dict. Canting Crew n.p.: Spill a small Reward or gift of Money.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1895		S.F. Chron. 6 June 11/5: I gives his buttons a warm spill.
1977		(con. 1941) R. Beilby Gunner 255: Gunner took the money as furtively as Whiteside offered it, his fingers reaching for the spill, sneaking it into his palm.

2. a drink.

1909

J. Ware Passing Eng. of the Victorian Era.