There's a reason why each state has them. Stop deploying them over seas (a.k.a not guarding the nation) and deploy them at home during disasters. Nothing wrong with other states (most likely neighboring) deploying their national guard units to aid in the effort. They aren't really currently purposed for this kind of work but it's not a wild stretch to square this kind of thing away. There's also nothing wrong with allowing them to take on civilian hands under their command for the task. I don't know why government agencies like to pretend that their weekend "training" which consists of watching PowerPoint presentations gives them some kind of super special powers that makes them better than civilians who would like to help in more direct ways than simply donating money.
And for these kinds of missions NO ARMED SOLDIERS! This is aid and rescue, not combat.
I think that's a pretty good starting point.