I actually applied to one school for psychology in case I didn't get into engineering; I loved to people watch and learn what made them tick just like how I loved looking at contraptions and wondered how they worked. I got to take two psychology courses at school too which I paid a lot of attention at and enjoyed but didn't do as well (damn multiple choice questions!).
Well those that can't engineer... manage... sales I'd probably manage people managing machines. I'd probably fill the design void in my life with a string of artistic hobbies. (Which I sorta do anyway.) Tough question for someone who goes through a business thinking 'gah your doing it wrong'.
Id be doing what I did part time through college ... modifying and building race cars and drag racing. Its a tough market to make big money, but you have a lot of fun all the time.
I would just be in a different field of engineering, probably electrical or software engineering. I can't imagine finding job satisfaction in anything outside of engineering; I just love the technical challenge and creativity of engineering.
For a hobby I now design and make fashion and costumes for theatres etc....but with some emphasis on the pattern making and the good fit of it. I'm also designing and making lace with again the emphasis on making patterns and new designs myself....so even in a more female oriented approach I tend to have a healthy interest for the technical side of the job.
I'd probably do something with landscaping. For one thing, I could use my industrial tire shredder to make some mega-awesome mulch, and for another, I love it when the yard comes together into a gorgeous place-anyone-would-want-to-be!
