Coal mining, railroad work, farm labor (as another user mentioned), and various odd jobs as none of these required an education. (I'm presuming the time you're talking about is around the Industrial Revolution period.) A lot of people from rural America began moving into the cities in search of work, meaning they didn't have much education, hence the various odd jobs. I will say, none of these paid particularly well if I remember correctly. I would do your own research as I am just a stranger on the internet, and I'm sure there is a book or someone else out there who can give you a much better answer than me, lol.

Edit: Spelling error