Marcel wants to know.
I've been racking my brain.
To help you if you come from somewhere unfamiliar with the saying, here is Wiki's opening on the subject: sliced bread is a loaf of bread that has been pre-sliced with a machine and packaged for convenience. It was first sold in 1928, advertised as "the greatest forward step in the baking industry since bread was wrapped". This led to the popular phrase, "the greatest thing since sliced bread".