My 18 yr old son would greatly appreciate those things listed here. Some other ideas would be the great fall back coupon idea, she could make coupons for him to cash in over the next few months, one would be wash his car (when the weather permits), a home cooked meal on the date of his choice.
Is he into sports, we have a farm baseball team here, tickets are less than $10 for lawn seats, due to go on sale soon, again give him a cute IOU, let him pick the date if need be.
How about a coupon for a picnic? Or even tickets for a local amusement park.
How about an invitation to what is normally a family event, camp out, etc.
One thing I do for my hubby is he loves to much on beef log and cheese, I purchase them, get out my trusty heart shape cookie cutter, cut the slices of meat and cheese into heart shapes and decorate a zip bag with hearts.
My son loves that I make a few for him as well.
Your daughter could have a few of her friends compose and give a cheer for him at an appropriate place and time of course. What about a homemade T with his fave subject?
OK out of ideas now.