At the very beginning of the game, you need to talk to a stalker named Wolf in the Cordon newbie camp. Behind Wolf is a ladder that leads to an empty backpack in the attic.

Climb the ladder but do not enter the attic. Instead, walk around the ledge formed where the roof and walls meet. You can work your way onto the roof of the house that way.

Once on top of the roof of this house, there is an identical house north of the one you are on. You can sprint and jump to the roof of that adjacent house (you take a little damage).

When you get to the second house's roof, carefully make your way to the side with a hole in the roof -- just past it, you should be able to make out a wooden crate you can destroy. If you spoke to Wolf and accepted the mission to rescue Nimble, you should have a pistol.

Shoot the wooden crate and a Stalker suit (worth 15,OOO Rubles) will be inside. Simply grab it and you'll be immediately better off than you think you could be!