Serving your nation is simpler than most people think. And no!, you need not be just in a military or politics to be able to do that. There are many many ways but I will give you only one.
Be extra mindful of yourself when you are with people not belonging to your nation. Throw that ‘be yourself’ crap out the window that time. When you are with them, you are ‘your nation’ for them. Whatever you will do, they will take that as ‘your whole nation’ does it. If you are already polite, be more polite with them. If you are already respectful, be extra. Or, if you are a guy who gives ‘no shit’, try to bring that attitude down when you are with them.