The first two boulders do not roll now, so go down the steps and enter the cave, lining Lara to the Shotgun Shells (two squares away from them). First, side-step to the square on the left hand side to trigger the boulder that is front of the column on the left. That way it will pass over the Shells.

You still have the entrance to the back of you, so step on the square ahead to trigger the boulder from the right and hop backwards to avoid it. Again, step on the same square ahead, then onto the next one to trigger another boulder that it will not come towards you.

Turn right to face the Shells (the entrance must be on your right now), step on the square of the Shells and hop back to avoid the boulder from the left. Pick up the Shells.

Turn around and walk towards the column.

Turn right (the column is on your left now) and run to the other side to trigger the boulder that blocks the exit.

Now freely go and get the Rocket. When you step on that square, another boulder rolls, but it is not on your way. Go and freely get the Desert Eagle Clips from behind the column.

Run to the exit without stopping, because a boulder comes from the right. Enter the alcove on the left and pick up the Grenades.