USB host devices are cheap and easy to come across. You can use a crap old PC with a fresh OS install, then wipe it. Or an old phone with microUSB OTG. Or a DVD player if you only need the file list (those can usually only open JPGs, GIFs, MP3s, and MPGs or AVIs with one of the video codecs allowed on VCDs/DVDs). Even some microcontrollers will have USB host capabilities and software libraries that will let you get the file list or contents slowly over serial.

If you're worried about "killer USBs" (data line zappers), open it and check for capacitors (and antennas in case they use Find My or LoRa for exfiltration but that would be super unlikely). Generating overvoltage inside normal-looking chips is technically possible with charge pumps and embedded capacitors but very expensive to pull off.