Originally posted by reh321 According to Wikipedia, the word "poke" came into English from French, and refers to a bag. Apparently, during the Middle Ages a farmer might try to sell an unopened / unexamined bag which he claimed contained a pig {source of bacon as you've already commented} but which actually contained a dog or cat {not as good source of bacon} .... so the saying "Don't buy a pig in a poke" actually means, in the words of a US president, "Trust but Verify".
I guess our "he bought a cat in a bag" is just the other end of the same deal, then.
But yes, I think "pocket" comes from the same French word.