It's easy to find local volunteer opportunities related to Homeland Security. Your local health department is just one organization that needs you. Why? If we were attacked with biological agents such as smallpox or plague, local health departments would desperately need hundreds of volunteers to help provide pharmaceuticals to the general public -- even if you have no medical experience. Most health departments across the country have been forming Homeland Security Volunteer Corps. Contact them and ask how you can help
Honor the Fallen by serving their families.
If you're looking to help out, you might investigate your state's defense forces. These are what amount to the National Guard Reserves - volunteer military forces, under the command of your state's governor, who defend your state when its National Guard units are deployed beyond its borders.
See here for a list. Each state's defense forces generally have a different name: the Maryland Defense Force, the Ohio Military Reserve, the New York State Guard, etc.
Keep in mind, btw, that these are official state militias, organized and operated by the state government, not screwy private "militia" groups run out of somebody's trailer. They are organized and run like the National Guard, except that state defense force members cannot be federalized or deployed outside their state.