Found: List of Things to Pack for a Cycling Trip
This so awesome I had to steal it from Chainthug.
It's a list of things to pack for a cycling trip longer than 100 kilometres but less than 300 kilometres. And he found it between an old cycling book "Cykling och Cykelsport" from 1934!
I'm not gonna translate the full list but the point is that while it's old it's also almost completely modern, just all the basic stuff you would pack with you today. Things like basic tools, spare tubes, some clothing, a tooth brush, towel, a clock (which is a MUST according to the list), a drink flask, a map etc.
And according to the list for a trip longer than 300km you may also want to bring along some extras like "a photography machine" and "a spare pedal and axle".