Useful summer activites

I want to major in engineering(not sure what kind yet) and would like some exposure to this field during the summer. I
don’t want to attend one of the programs at colleges because they are too expensive. Does anyone have any recommendations as to what I can do that is inexpensive, but also looks good on college applications?

Anything you do is fine as long as you do something! If you work, colleges understand that earning money is important and that is totally fine. If you volunteer, find a place/cause you feel strongly about and that is valuable as well.