from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A bag whose contents are unknown.
- n. A surprise package randomly picked, a lucky dip.
- n. A non-specific mixed lot of a product at the supplier's choice.
- n. A sausage.
- n. A pie.
From mystery + bag. (Wiktionary)
From 19thC British Rhyming slang for snag ("sausage"), influenced by sense “bag whose contents are unknown”. (Wiktionary)