Music format for bringing to audition/demo


Had my system for 20+ years, time for an upgrade. I have not been in a hifi shop since 2000 and at that time I would simply bring CDs. Nowadays is it most common for people to bring digital music on a thumb drive or some other way and what is that? Or do people rely on dealers having nice streamers and they just look up what you want to hear? 

Basically I want to know what it most common and how I can bring music that say I downloaded from hd tracks or similar sites to the dealer. 
nhb1
I haven't felt the need to bring anything in years. If you have something you feel the need to hear in order to be able to evaluate, then bring what you feel you need. Why would you bring what someone else thinks they need?
If you feel the need to bring your own music when auditioning speakers just bring your favorite music on whichever format you generally use. No use suggesting classical music on reel to reel when you’re a headbanger that listens to MP3’s.
OK I will just bring some downloaded 24bit songs on a thumb drive, just wanted to check what was common or if there's another way I should know of that's better.