Second shelf down: the CPU shelf itself.
Third shelf down: RP bus magazine and tall blanking plate where the maintenance unit (MAU) would be if this was a B-side processor rack.
Bottom shelf: RP bus magazine.
The little green light on top of the rack indicates that this rack is the Executive processor, the processor that is primarily handling the traffic being switched at the time of taking this picture. The blanking plates were always used to increase the cooling efficiency.