All the stuff he would need to know to run a household. Budgeting, grocery shopping, menu making, cooking basic skills, cleaning, laundry, hygiene, sewing a button or hem, etc. We also took care of "babies" in home ec - we decorated eggs to look like babies and had to carry them around with us for a week.
You know your child's limitations so whatever you think he can handle but I would teach him the skills he would need as if he were going to be moving out and living on his own. That would all qualify as home ec. I'd also include basic checkbook/bill pay skills in that - I always felt like that should be a part of every child's basic education and can't understand why they don't teach it in school.