Monument Island - behind the desk in a room with the Siphon.
Park Ticketing - inside the ticket room (you can collect this item after you've separated with Elizabeth).
Soldier's Field Greeting Pavilion - on a desk in the security office you can gain access to only by breaking in.
Soldier's Field - inside a secret cellar of the Fellow Traveller bar. The main character can access this area by completing the only side mission of the 8th chapter.