'Mark 1' Ambu Compact Resuscitator.

Pictured here is a 'Mark 1' Ambu Compact Resuscitator (Ambu-bag) complete with it's carry satchel and instruction manual.
Most will no doubt remember that the satchel hung over the oxygen bottle in a lot of PAS vehicles. The county (HAS) vehicles had a slightly larger leatherette version of the bag, which also contained an ambu foot-aspirator, and in most vehicles this was stored in the overhead locker in the saloon.