soft drink, 1909, shortening of brand name Coca-Cola.

coke (n.1)

"residue of fuel," 1690s, northern English dialect, perhaps a variant of Middle English colke "core, charcoal" (c. 1400), itself possibly related to -colc, an Old English word for "pit," which perhaps would give it a sense of "what is left in the pit after a fire."

coke (n.2)

shortened form of cocaine, 1908, American English.