The central, metal block (sector 51) at the northeast of the map bears two lightning bolts on its eastern side instead of one. Press on that side and it will lower to unveil (skill dependent) six/five/three sets of shells, seven/five/four stimpacks and a backpack.
Routes and tricks
This level contains a "teleporter" exit, which means a death slide could possibly be performed on this level in the exit hall. Whether it would make the level take a shorter time to complete or not is presently unknown.