When the ancient Romans shipped an obelisk across the Mediterranean from Egypt, they packed it in lentils.
You wondered about the source for an anecdote about Caligula shipping an obelisk to Rome packed in beans. It happens that I know the source for this one, since I was just reading about Caligula's obelisk freighter in studying for a test on Ships and Seamanship in the Ancient World. Lionel Casson mentions it in "Ships and Seamanship in the Ancient World" (1995 edition) pp. 188-189. He cites Pliny, NH 16.201 "nave, quae ex Aegypto Gai principis iussu obeliscum in Vaticano statutum" etc. Casson translates the lentils as "ballast" not "packing" and estimates a load around 1300 tons burden. Apparently the ship sat in Rome afterwards until Claudius filled it full of concrete and sank it for a breakwater. I can't find it online, but it looks like Wikipedia etc. are right for once.
Pliny (16.76.201) says that the obelisk erected by Caligula in the Vatican Circus was brought from Egypt by ship with 120 modii of lentils pro saburra ("as ballast" and thus not as packing material). The lentils are absent from Pliny's other mention of the obelisk (36.15.74).
PLIN. nat. 16, 201 CXX modium lentis pro saburra ei fuere.