Cigarette Case is personal Preparation item of Haru.
When in inventory, it has a 15% chance to add 1 Cigarette to your Cigarette counter on top bar of game UI after you investigate a location, but before the game starts an Event or Combat encounter.
If this effect triggers, the message 'You smoke an old cigarette from your CIGARETTE CASE...' will be added to the message log at the bottom of game UI.
Synergy[]
Haru's starting perk, Hard-Knock, runs on Cigarettes (the counter). Cigarettes (the item) and its foreign variant are pretty costly and depend on your access to Shop, Vending Machines or Illegal Den, so the Case only helps Haru in the long run.