Bread itself isn't exactly a technological wonder. For some reason, however, the phrase "the best thing since sliced bread" persists as the preferred way to say that an invention is cool. Prior to 1928, if you wanted to say that a technological innovation was impressive, you had to think of your own way to say it, rather than falling back on this tired cliché. Not having this phrase in our lexicon would be the best thing since ... we'll get back to you on that.
There Was No Sliced Bread