I don't recall what we got our daughter. I think we had a family trip to the coast and we probably got her a $100 gift. We then spent several hundred dollars getting food, necessities, and decor for her dorm at BYUI.
When I graduated, I got the big baseball book of statistics (I think it was $50) and my parents got me a sweatshirt when they dropped me off at Ricks.
I also have friends who've taken their kids to NYC, Europe, Hawaii, and more for their senior vacation. Even if we had the budget for that, that seems like overkill and spoiling your child.