The Amazing Treasure Hunt
Write him a long love letter. Put it in a very fancy hand-decorated envelope.
Now hide it. Write a clue to where that hiding place is. Now hide that clue somewhere. Write a clue as to where that clue is hidden. Hide THAT clue. Repeat.
Basically, you are creating a fun excursion day. You can even select places of business or friends to hold clues he can only get if he figures out the person and does something silly.
"Go to the boy who makes me laugh about sports and tell him you farted in the bathtub this morning. He must not be alone when you tell him."
That kind of thing. Make 10-15 steps out of it, and when he finally gets the letter, the event itself is the gift, the letter is a memorable payoff.
Be a fun girlfriend.