Depends on what age you are and what the options are around you! I guess the go-to music work experience is to be a music teacher for younger kids and just teach them the basics of whatever instrument you know. Neighbours, family friends and relatives would be a little less nerve wracking.
I work at a second-hand instrument/vinyl/hi-fi store as I wanted to learn how to repair instruments/basic retail experience. As I'm under the age of 16 I can't work at chain stores or anything, but you can probably show your resume to any small music stores/record stores around you that need an extra hand. As long as you have decent musical knowledge (it helps if you have a cultured taste) and that getting paid well isn't the most important thing, it should be fun. Unless they specifically ask for it, try not to go through every single one of your musical credentials and concerts as it can make you look a bit desperate.
I'm pretty sure you can get some money for making basic music tracks on fiverr/other freelance work as well. People pay for things like basic lofi tracks/background music, but if you want a more reliable source of experience, I still think the other options are better.