Assuming I had a boyfriend, I would enjoy him taking me somewhere unique where memories can be made. Maybe an airshow, and a customized banner on the back of a plane with a romantic message to me. Or spending the whole day waiting on me hand and foot and treating me like royalty. Or take off work just to stay home and be with me.
Physical materials, I wouldn't mind an old photo of one of my very special relatives from years ago in a new frame. Better yet, just spend the day going through old pictures and just having a good time laughing at the good times.
Hahaha I'm such a hopeless romantic lol.