"large bag," Old English sacc (West Saxon), sec (Mercian), sæc (Old Kentish) "large cloth bag," also "sackcloth," from Proto-Germanic *sakkiz (cf. Middle Dutch sak, Old High German sac, Old Norse sekkr, but Gothic sakkus probably is directly from Greek), an early borrowing from Latin saccus (also source of Old French sac, Spanish saco, Italian sacco), from Greek sakkos, from Semitic (cf. Hebrew saq "sack").
The wide spread of the word is probably due to the Biblical story of Joseph, in which a sack of corn figures (Gen. xliv). Baseball slang sense of "a base" is attested from 1913. Slang meaning "bunk, bed" is from 1825, originally nautical. The verb meaning "go to bed" is recorded from 1946. Sack race attested from 1805.