The easy answer is not to look militaristic at all!
My packs are civilian book, camping, climbing, hiking or school packs be it a fanny or backpack. For me it’s mostly an old Mountain Smith fanny pack that I have traveled the world with and never had any one look twice at. One of my bags got looked in once during a border crossing. The officer looked up and asked camping gear? You bet I love it, I told him with a smile.
But like others mentioned I am clean cut and dressed properly for the environment and make sure I do not attract attention to myself.