JeniSkunk: A game manual is NOT a 'goodie' or 'extra item'. It is an essential item.
Kerebron: Less and less so. In "good old days" of Good Old Games, most of the games were offered with manuals, maps, artworks, soundtracks, etc. all included in the base package. Now all these items are either non-existent or paid extra.
Since these older released games are still being offered on GOG, the physical printed media they were released with, should always be part of the base download package, and not a 'goodie' or 'extra item' for separate download.
As an example a game I have multiple physical copies of as well as the GOG version, The Elder Scrolls III Morrowind.
Included with the game is a detailed printed manual, and a poster size printed map.
Those aren't bonus luxury extras. You do need them especially when starting out in playing.
But for the GOG release, the manual is an 'Included Goodies' item for separate download, and a copy of the map is non-existent.
What is a valid 'Included Goodles' item with the GOG release is the 'GOTY Guide' or more correctly The Morrowind Prophecies - Game of the Year Edition. As a physical book, that strategy/hint/walkthrough guide was a separate purchase to the game, so having the PDF of it as an 'Included Goodie' is valid.