Hi there!
I volunteered in a charity shop (also for a hospice) for nearly two years and I'm about to start a politics degree.
Yeah, it may not seem super relevant but it shows that you are a well-rounded person, especially as it is a combination of charity and a job. It shows you can learn new skills. It's not like it's the only thing you can do. In the holidays, you can volunteer at a hospital, you're not bound to the charity shop. Just work experience won't get you far.
Medicine is INCREDIBLY competitive (one of my best friends is about to start her medical degree). Thousands of others will have the grades needed, but universities look for a well rounded candidate. You need to have more interests than medicine. I loved working in the shop, especially since it was going towards a charity I truly care about.
Best of luck! Feel free to message me if you need any advice about working in a charity shop x