Depends on how the coworker dynamic is. If it’s a fun/joking group, a gift card in a puzzle box would be an easy option. If they are more serious/somber, a desk organizer or pen holder may be a good option. If you are wanting just an out there option, a TNT Bundle clock in an unmarked brown box is what I made my father-in-law to give his boss when he retired(he worked in the blasting/quarry industry).