You may disagree with our answer, in part because there were many things better than wrapped bread in the long history of human existence.
However, when we look at where the phrase “the best thing since sliced bread” came from, we can see that it arose from a specific marketing claim.
In 1928, Otto Rohwedder of Davenport, Iowa, invented the world’s first bread-slicing machine. Several companies began to use it to create prepackaged sliced bread, which was advertised as “the greatest forward step in the baking industry since bread was wrapped.” That advertising slogan led to the now-famous phrase “the best thing since sliced bread.”What Was the Best Thing Before Sliced Bread? | Wonderopolis
So, we can conclude from that statement that if sliced bread was the best thing since “bread was wrapped”, then the best thing since sliced bread must be – wrapped bread.