It sounds like your therapist does not yet know that your next session will be the last? Or am I misunderstanding this? If he doesn't know, my suggestion would be to contact him and give him a little warning about this. Being taken off guard is not always pleasant. It's one thing if you disliked the therapist, but you indicate that you definitely like him.

I think your ideas and some of others' are very nice. If your therapist was a female, a nice bouquet of flowers would be a suggestion. Or maybe your male therapist even likes flowers? I know of stories where patients have given therapists or psychiatrists pieces of their artwork or a poem, or the like.