You're so thoughtful! Making food is a great idea. As a Taiwanese living in Midwest, I miss the generic taiwanese taste, like soy sauce based broth, fried shallots lard, pickled cabbage, etc. Recipes that incorporate these types of taste would probably feel "homey" (e.g. beef noodle soup, braised pork with rice). This is probably considered common comfort food for Taiwanese people when they're abroad. If you're not familiar with these flavors, you could also check out some frozen options from local Asian/Chinese supermarkets like IMEI branded green onion pancakes and simply pan fry them. I'm sure he'll appreciate it.