Well, you're definitely right that he would love whatever you do for him... but it doesn't really help in making a decision, does it? Hmm.

He likes making other people happy. Making them happy makes him happy. But that means he doesn't tend to do a lot for himself. I know he enjoys going out for ice cream. You could do that... Or maybe set up a sort of create-your-own-sundae bar and have a night in? He always seems really appreciative when someone else cooks for him. I could find you some recipes, if you thought you might like to do that. Ah...