Most Helpful Girl
Something home made is sweet and sentimental without being too serious or too expensive. You want to strike a balance of being sweet and playful enough to make him feel special, without making a big deal out of anything.
You could make him cookies in the shape of characters from his favorite movies... like Star Wars. Yoda cookies? BB-8 cookies?
One year I painted my new boyfriend at the time a little handmade card with a heart made of square blocks, to look like a pixelated computer screen, and put "with every bit of my heart"... he was into computers and he loved it. He put it in a frame on his desk which made me feel great, too. It was such a small gift, silly and sweet... but that was the right tone for our new relationship at the time. I was so glad it worked out well!
I'm sure you'll come up with the perfect thing :)