Go places.
Bring things and people in.
Visit friends of yours who have cool stuff or do interesting things.
Ask him to go with you if you take the dog to the vet. Drive home different ways and take your time.
Putz around. Go to the mall some morning when it's not at all full of teens and window-shop.
If you can at all afford it, find something in another town like a play, concert, museum, event and take him there. Stay overnight.
Go touristing somewhere not too far from you. Like if you had out of town guests, but just go with your son.
Watch DVDs together.
Is there something you do that he might want to learn? Is there something you could learn together? Maybe the two of you could take a class or join a group that does... photography, hiking, quilting, scrapbooking, pottery, woodworking...
When Marty and I were going to the credit union to get money to get a used Jeep he wanted, I took Holly and her boyfriend along. That was a learning and sharing experience for us all.
photo by Sandra Dodd