When in the Library, the two rangers will announce the titles of several books. One of them is "Roadside Picnic" (1977) by the Strugatsky brothers, which was the book that Andrei Tarkovsky's 1979 movie "STALKER" was based on, which then was the inspiration behind S.T.A.L.K.E.R. Shadow Of Chernobyl.
The first person you can talk to resembles a "loner" Stalker and says "Take it easy bro!"
The scene with the campfire with the guitar.
The winter mask that are on dead people.