These people send out trucks to collect unwanted items for local charities. I assume they're legit, altho they always seem to be collecting for different organizations every time they call.
Not a scam at all. They are annoying because they call so often, but they are an arm of a 501(c)(3) organization that helps veterans, including the proceeds from their thrift stores (in the same vein as Salvation Army, Goodwill, St. Vincent dePaul).