The gifts for congratulating classmates on their promotion can be daily necessities, food, or flowers. But it should be noted that it is not appropriate to give sharp tools such as knives and scissors, as well as private items such as pajamas and bathrobes.
The most popular promotion gifts should be practical items that he is reluctant to buy but likes very much. If you are reluctant to buy them, you can also buy something that can be placed in the host's home frequently so that the classmate can remember you, such as a life-like doll, a mural, or a model that the host likes.
Another thing is to see if he has children, and what the children or his wife need. If he doesn't have a wife, you can give your classmate one:)
I hope my suggestions can give you some inspiration.