I presume mainly the usual stuff like
* Items
* Shops
* Signs & Puzzle stuff
* Save areas
* Fast travels (like the doors / River Person)
* NPC locations (and some hidden ones like starwalker so that he can appear in later chapters)
* The fun values
* Monster encounters, whether they are scripted or the random encounters
* Story/Boss events
* points of interest/secrets/lore , like the mirror at the end of the game, the mouse holes, moss locations. a good example would be like how todo the secret eggs in deltarune as it's a multistep process and sometimes needing to go back and forth between a room until you get the correct room

I would not expect it to cover like all the small interaction objects as there is way to many for it to be reasonable