Ideas to consider: "cool" t-shirt, sports jersey, or a hoodie, modern board games (King of Tokyo, Sushi Go Party), something activity related (a balance board, sports towel, new sports bag, sleeping bag etc.), fun snacks and drinks (just fill a box with some interesting sodas, flavoured popcorn, chips and other treats), emergency phone battery, musical instrument stuff (drum sticks for a drummer, etc.), Pocket Disc flying disc (like a crocheted frisbee that can be tossed into a backpack or pocket),
Lego or Nanoblocks, graphic novels or other series books, jigsaw puzzle, or a cozy blanket, If your son enjoys Rubik's Cube, he may enjoy some other puzzle-type games. Think Fun makes a lot of different ones. Rush Hour is pretty good.
One idea I have used for my daughter was to pick her up her own special mug and bowl. The ones we have are hand-made and painted by a young potter with fun graphics on the side, but you could find something that perhaps appeals to your son. She pulls her dishes out of the cupboard every morning when she has cereal for breakfast. I'm not sure if something like that (a personal popcorn or ice cream bowl, perhaps?) would appeal to your son or not. (You could always add a jar of chocolate sauce and some ice cream sprinkles to an ice cream bowl, or some popcorn flavouring and popcorn to a personal popcorn bowl.)
Amazon sells ice cream spoons that say "My ice cream spoon," but I have seen places online that will personalize ice cream spoons as well.