It depends for me, like Bill has posted, both individually and on the large scale. I see not the slightest reason to differentiate between personal and national reaction.

(1) If I'm about as strong as the aggressor that is if counteraggression makes sense, fight back. (Tit for tat is on the long run the best survival strategy in computer simulations)
(2) If the aggressor is much stronger and/or fighting back makes no sense, then do exactly what Bobert describes as his action on a national basis (but as a general rule it makes no sense: I just try to imagine Luxemburg attacking Germany and then have to smile about Bobert's overly general response). On a personal level too, I'd hand over my money and whatever they want to a group of strong and armed robbers when nobody is near to hear me.
(3) If the aggressor is much stronger and makes clear that my death/destruction is his aim than I'd fight back against all odds to make him at least rue a bit his killing me, both on a personal and on a national level. A group of thugs about to kill me, I'd at least try to kick one of them where it hurts. My favourite group of people in history doing such a fight are the Jews in the Warszwa ghetto fighting without a real chance against the German army but trying to die with a fight and not like lambs and trying to kill as many of their eventual murderers as possible. This too for me is a situation in which Bobert's (in general) good idea simply doesn't apply.

I'm a conscientious objector (after having served my time) but not for being a pacifist, but simply for considering fighting back in the particular context of a nuclear war in Europe senseless. In different political contexts I would not have objected.

Wolfgang