1640s, "a gathering into a bundle," verbal noun from bundle (v.). Meaning "sharing a bed for the night, fully dressed, wrapped up with someone of the opposite sex" (1782) is a former local custom in New England (especially Connecticut and southeastern Massachusetts). It was noted there from about 1750s and often regarded by outsiders as grossly immoral, but New Englanders wrote defenses of it and claimed it was practiced elsewhere, too. It seems to have died out with the 18th century.
I am no advocate for temptation; yet must say, that bundling has prevailed 160 years in New England, and, I verily believe, with ten times more chastity than the sitting on a sofa. I had daughters, and speak from near forty years' experience. Bundling takes place only in cold seasons of the year—the sofa in summer is more dangerous than the bed in winter. [The Rev. Samuel Peters, "A general history of Connecticut," 1782]