That outfit was the typical garb of a merchant seaman during WWII. Well, maybe a black watch cap instead of the one he was wearing.
Re the photo in your post #16...Wikipedia (again) — “Guthrie believed performing his anti-fascist songs and poems at home was the best use of his talents; Guthrie lobbied the United States Army to accept him as a USO performer instead of conscripting him as a soldier in the draft. When Guthrie’s attempts failed, his friends Cisco Houston and Jim Longhi pressured Guthrie to join the U.S. Merchant Marine. Guthrie followed their advice: he served as a mess man and dishwasher and frequently sang for the crew and troops to buoy their spirits on transatlantic voyages. ... In 1945, Guthrie’s association with communism made him ineligible for further service in the Merchant Marine, and he was drafted into the U.S. Army.”
As Maine Mariner says in #20, that’s his Merchant Marine garb, not an affectation.
Marine and longshoremen unions in that era were completely dominated by communists. I’m sure he fit right in. Of course, that’s true of unions to this day. After all, communism has its roots in the workers throwing off the shackles of the capitalist bourgeoise class.