The first movable crate is on the left of the stack. Go to the left side of it and pull it once. As you face it, go to the left between the barrels and push the same crate next to the entrance. Then pull it in front of the entrance.

Now pull the second movable crate from the stack once (to position it where the first one initially was) and go to the backside of it to get some Automatic Pistol Clips.

Climb on the crates and pull the top left crate. Pick up the two sets of Harpoons beneath it. To unblock the entrance, push the first crate into the corner.