To be honest, I would never even consider buying a USB drive at a gig. Though I suppose maybe if you packaged it nicely - on a card with some interesting artwork?

I think I'd be more likely to buy a CDR: if you are only playing a handful of gigs here and there then it's not too much effort to just burn some CDs yourself, stick labels on them and print off some covers.

But you should DEFiNITELY set yourself up with a Bandcamp page. That's how I discover, listen to and purchase most of my music. It's silly not to.

Here's an example - one among hundreds I could link to - of an exemplary bandcamp page:
Adam Kiesling's old-time music bandcamp page