An 1850's term to reference 'sausages'. The 'mystery' was due to the fact that nobody but the maker of the sausages would know what was in them, and the 'bags' were the guts which contained the chopped meat.
“Hi, Butcher Barry. I'll take 6 steaks and a few Bags O’ Mystery if that's okay.”
(Noun) What a Catholic priest offers an alter boy to get the taste of semen out of his mouth.
Now now don't cry I know that stuff doesn't taste great but here is a wee bag o' chips and a coke. Remember it is our secret.
(noun) synonym for extra large, extra salty, extra greasy, bag of potato chips
Mary: Henry watch ur diabeetus!
Henry: I wanna eat mah bag o' beetus!
*munch, munch, munch*