As @jrixn1 says, it would depend upon what amp you have.
However:
1. An MP3 player, laptop, tablet or mobile 'phone would be suitable;
2. USB stick would work as storage for your music if you're using a laptop. An SD card / micro SD would be suitable for tablet / mobile 'phone;
3.Dependent on if your practice amp has an 'aux in', or 'MP3 in' socket, use this for the source music.
I use either a Promethean P20:
Or an Ashdown Tourbus:
And use a small tablet with Spotify & MP3 tracks stored to the Micro SD card, using the headphones socket.