and the winner is ...

it dawned on me that the best thing before sliced bread had to be unsliced bread.  just because something becomes sliced and changes in no other function doesn't thereafter enter it into the Best Thing Since Hall of Fame.  it had to be there before, too.  so, we're left with - What was the best thing before bread?

i guess we can get some insight from that great black hole of unsubstantiated fact, wikipedia: The earliest archaeological evidence for flour, which was likely processed into an unleavened bread, dates to the Upper Palaeolithic in Europe, around 30,000 years ago.  which raises the issue of sliced bread - i doubt slicing unleavened bread is what is so profound.  it had to be leavened bread for which slicing became something to admire.

the plot thickens.  again, the same wikipedia link: Although leavening is likely of prehistoric origin, the earliest archaeological evidence is from ancient Egypt. Scanning electron microscopy has detected yeast cells in some ancient Egyptian loaves. However, ancient Egyptian bread was made from emmer wheat and has a dense crumb. In cases where yeast cells are not visible, it is difficult, by visual examination, to determine whether the bread was leavened. As a result, the extent to which bread was leavened in ancient Egypt remains uncertain. 

ok, then, we learn nothing.  let's try this: Pliny the Elder reported that the Gauls and Iberians used the foam skimmed from beer to produce "a lighter kind of bread than other peoples.

pliny?  ayep.  read here.  life was kinda boring, but that takes us back to 50AD or so.

now, the best thing since leavened bread?  take your pick:

1st century: Buttress dam in Roman Empire

1st century BC: Segmental arch bridge (e.g. Pont-Saint-Martin or Ponte San Lorenzo) in Italy, Roman Republic. Arch dam (Glanum Dam) in Gallia Narbonensis, Roman Republic.  150 BC Astrolabe invented in the Hellenistic world. Before 71 BC (possibly 3rd century BC): Watermill (grain mill) by Greek engineers in Eastern Mediterranean (see also List of ancient watermills) 

2nd century BC: The earliest fore-and-aft rigs, spritsails, appeared in the 2nd century BC in the Aegean Sea on small Greek craft. Here a spritsail used on a Roman merchant ship (3rd century AD).  Finery forge in Han Dynasty China, finery forges were used to make wrought iron at least by the 2nd century BC in ancient China, based on the archaeological findings of cast and pig iron fined into wrought iron and steel found at the early Han Dynasty (202 BC – 220 AD) site at Tieshengguo. 2nd century BC: Paper in Han Dynasty China: Although it is recorded that the Han Dynasty (202 BC – AD 220) court eunuch Cai Lun (born c. 50 – AD 121) invented the pulp papermaking process and established the use of new raw materials used in making paper, ancient padding and wrapping paper artifacts dating to the 2nd century BC have been found in China, the oldest example of pulp papermaking being a map from Fangmatan, Gansu. 

 3rd century BC: An illustration depicting the papermaking process in Han Dynasty China. Early 3rd century BC: Canal lock (possibly pound lock) in Ancient Suez Canal under Ptolemy II (283–246 BC) in Hellenistic Egypt.  3rd century BC: Valve Tower Sluice in Sri Lanka.  3rd century BC: Water wheel in Hellenistic kingdoms described by Philo of Byzantium (c. 280 – 220 BC). 3rd century BC:Blast furnace using Monsoon winds in Sri Lanka. Earliest example from the 3rd century BC, although most sites date from 1st millennium AD.  3rd - 2nd century BC: Blast furnace in Ancient China: The earliest discovered blast furnaces in China date to the 3rd and 2nd centuries BC, although most sites are from the later Han Dynasty. After 205 BC: Dry dock some time after Ptolemy IV (221–205 BC) in Hellenistic Egypt.

hunh ... so much from which to choose!  of course, the grain mill stays with the bread theme, but that's not necessary.  i'm rather fond of pulp papermaking, but then the blast furnace has to rank up there.  i can't pick.

wait.  won't cop out.  ok, i'll drift a bit further back:  5th - 4th century BC: Traction trebuchet in Ancient China between 5th - 4th century BC, appeared in the Mediterranean by the 6th century AD.

there. the best thing before sliced bread was leavened bread.  the best thing before leavened bread was the traction trebuchet.

done.