What did Luke wear between Episodes IV and V?

[Prime Clone]

As with all people, he likely wore what was suitable for the environment he was in.

Y'know, the more I think about it, the more this very first response to the thread makes the most sense.

Luke's Tatooine outfit was very specifically adapted to the desert conditions - it just wouldn't suit any other environment. Likewise, in freezing cold climes like Hoth, the Rebel snow gear is the obvious choice. Then there's the "GI Joe spy" type outfit from Splinter of the Mind's Eye, suited to cool, moist conditions.

This leaves the "ceremonial outfit" or X-wing ground uniform ("Bespin fatigues") as his default outfit, depending on whether he was on a flight mission or not.