I can't say as to what it might've been like 80+ years ago, but years back I was with a friend on a trip through a PX and there was a rotary display (perhaps like you might see used for postcards in other contexts) with rank insignia and other small uniform bits for fairly low prices (single-digit dollars iirc, though this was 20+ years ago). Even if they had to pay out of pocket or deal with an irritable quartermaster, the urge to give a small remember-me-by token to a friendly (and let's be honest, beautiful) face when facing down imminent chaos and barbarity is probably strong. Similarly, I recall hearing of troops throwing their coins to kids along the embarkment route in the UK as they headed to Normandy; after all, where they were going they wouldn't need them.
The display probably exists just because soldiers need that stuff, as a practical matter.
When they're required to be in uniform, then that's a requirement.
So if yesterday a uniform got ruined (by whatever mechanism that happens -- shit does happen to clothes sometimes), then today they can scrounge together another one.
Or they put together a spare one.
Or whatever.
(But it certainly is romantic to think that extra uniform parts exist for sale primarily to give as keepsakes to the Betty Whites of the world.)
