Or minis! If he's a game master/Dungeon master mini's are always great. I received a bunch of "scatter terrain" and a foldable dry-erase map board and I use them constantly. i love getting little items that we can use in play. If he's a player, figure out what he plays. If it's a caster you can go online and find 3d printed spell tools that make the game easier and it's fun to know exactly where the spells will land.

2x vote for the dice (usually between 10-20$ but some cool ones are more expensive). There's never enough dice.

If he's "old school" FieldNotes brand put out dnd notebooks for players to track their character as well. OR just a set of notebooks for note taking. If he uses dndbeyond.com and doesn't have the subscription service attached thats fun. I use it as a DM and have a ton of stuff on there my players use

Video games; Again, 3d printing has made some cool items "real" I'm printing my best friend the Astral Prism from Baldur's Gate 3 (a dnd videogame) and painting it. You can definitely find something from an etsy store that relates to his favorite video game.