My first job was as a receptionist at Great Clips--I greeted customers, made appointments, cleaned, did laundry...and swept hair. Ew. But I was 15, my prospects were limited.
After that I worked at Publix (a supermarket chain in the southeast). I worked there through college, in customer service. It seems like a completely irrelevant job, but it actually has helped me get jobs. Any experience working with the public is valuable. People I've interviewed with have actually commented when they see my resume, "Publix--they have GREAT customer service!" Also, working with a ton of cash on a daily basis shows responsibility and trustworthiness.
Anyway, while in college I also did a work study job at the library...which led to my current career path! My favorite job by far. :-)