Hay making
I had worked as a hay carter and shed stacker since I was about 13. Really hard work.
Then when I finished high school at 17 before I went to uni I worked the summer making hay. We worked every day for about 10 or 12 hours unless it rained - my luck, it didn't rain for three months. But it paid for my uni expenses. I think I've still got the abs from those days of hard work.