I'm currently volunteering at the British Heart Foundation charity shop in my town on the weekends. I usually work at the till, but I've also done some manual labour type things, like shifting about boxes of donations and then sorting through them. My shift is usually six hours long, with a lunch break around noon. Of course I'm not getting paid but I've found employers, especially in retail, like to hear about you volunteering like this; the experience is valuable. And I guess you could even use the manager at the charity shop you'd be working at as a reference if you needed one for a paid job.