If you fall in the big pit at the beginning of The Subway, there will be some rocks that are under the safehouse.

You must jump on the small one first if you want to get on top of the other rock. Once done, you can head back to the saferoom and repair again.

Tip: This is good for people who need another med kit in easy because you don't see any kits in the middle of the level or in the health boxes on the walls.