Okay, but why not have the cab drive him to the bus station? Or Ruby's place. Or Walker's house, et cetera? Why walk to wherever he was going?
He goes to his room, retrieves his loaded revolver (apparently), he takes 10 or so extra bullets, he had left nearly all of his money that morning for Marina. Why not keep $50 for his flight? Fifty dollars in 1963 is about $350 today.
FWIW, I think he didn't believe he'd survive the attempt. So once he did he was winging it.
I don't know that much about this aspect of the case so I can only give general impressions.
Oswald returns to his room to collect his gun and change his clothes ( apparently).
Bill's suggestion that he takes the cab past his room so he can check if the authorities are waiting for him makes sense in terms of a narrative in which Oswald is on the run. His change of clothes also feeds into this narrative.
I agree he is "winging it". His lack of money hints at a lack of preparation.
I get the strong impression that when he leaves his room he is heading for a specific destination but changes direction after the shooting of Tippit.
I'm just trying to get a handle on where he is heading once he leaves his room and a bus station that will get him out of Dallas is a good bet in terms of the Oswald-on-run narrative.