A G.I. bill (post-Korea) Harvard grad who saw the film with a 'Cliffie told me she had an opinion why Hal was so attached to his boots (which were noticed by Kim Novak in one scene). The 'Cliffie said Hal's frequent polishing and upkeeping of said boots was sublimated masturbation-:). It seems very Freudian... (Did Freud have an opinion about boot schlepping?). (Boots played a prominent role in one character's fetish in Luis Buñuel's "Diary of a Chambermaid" and Luis explored aberrant behavior, did he not?)
Freud in many respects was a dirty old man who had the temerity and lacked the common sense to psychoanalyse his poor daughter, Anna. He filled her mind with masturbation: the idea of masturbation, the "will" to masturbation, even when there was no such will, but Anna would respond in ways she felt would please the Oedipal Father Sigmund... I think he ruined her adolescence and even her adulthood.
Freudians are stereotypically sex-obsessed. The infection runs through any subject they put under scrutiny. I read a book by a Freudian, a book about fairies and such, and the author said that rubbing the Genie's lamp was a masturbation symbol, because after you've rubbed it enough, you are rewarded with the Something Wonderful that flows from its spout... oh, the greasy perversion of the Freudian mind!
As to Picnic, I think it's much simpler: Hal's boots do the walkin'. He's a ramblin', amblin', shamblin', travelin' man. Except for a freight car, Hal's boots are the main vehicle for his nomadic lifestyle. They carry the man and enable him to do what he does best (at least until his arrival in town, when he begins to want to settle down) - which is keeping on the move, move, move. So his boots represent his sense of freedom and locomotion.
If a Freudian interpretation is forced on Hal's boots, it needs to explain why and how they must be seen as phallic - when they are really located too far below the waist to be penis-symbols, and contradictory to the penis, they are meant to be filled and penetrated, while the penis itself is supposed not to be filled, but to fill and penetrate. I can only lament the generations who took the Freudian scam so seriously and all the funds they expended on his hogwash.
Hal clearly states that he inherited those boots from his father and fondly remembers pulling the boots off of his father's feet at bedtime on a nightly basis.