When I started flying we generally wore No 2 trousers under the flying suit and No 2 jacket over the flying suit. It went without saying that we went to the aircraft with shirt and tie and SD Hat.
Later this was upped to No 1s, jacket over flying suit - very smart with the blue FS underneath
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Then on the Vulcan Mr Roe very thoughtfully provided an SD Hat stowage for the Nav Rad and AEO. We also used to carry a rather large folding garment carrier into which 5 sets of uniform were stowed. At Prestwick on day dark we emerged from our aircraft in our No 2 Zuit Suits whereas the Boss's crew next to us only had flying suits. As I was properly dressed I was despatched to the terminal to buy toothbrushes etc - for them.
By the time I regressd to Shacks I used to carry a complete set of Civvies in my para-bag. Rather more useful and used quite frequently.
In 6 months in Acsension, despite orders to the contrary, no one wore hats except the 3 sqn ldr, the maj, the 2.5 and the Commander.
Now it is a 'hunt the hat' on rare occasions.
Headress OTOH, like Occasional Aviator is a necessity to stave off wind burn. However a grateful Air Force meets my needs with a free baseball cap emblazoned Royal Air Force.