I am going to DC in a few weeks. Staying in the suburbs and I will be taking the Metro on two days into DC . Going to Arlington and one museum. I would like to carry some type of self defense tool. I know that guns are out of the question. Is there a blade size restriction? Can I carry mace? Wish that I would have went ahead and got one of those Cold Steel sticks. On the day trips into D.C., I plan on taking a backpack with water, food and medicine kit. Also a folding map and cash. I don't want to rely on the smartphone and credit cards in case of disaster. I am thinking post 9/11 as worst scenario. Any thought or suggestions, I would appreciate.