Big cities have all kinds of people dressed all kinds of ways, all the time. Unless you're streaking naked, dressed like a street-walking prostitute or wearing a professional sports uniform in DC, you're unlikely to stand out.
Anyone who has gotten a glimpse into my ample car gear knows that I'm an outdoors enthusiast (i.e. backpack, boots, hiking poles, paracord...) and like to be self-sufficient in regards to basics like tire air compressor, jumper cables, etc.
No one has shown a propensity to rifle through my stuff. If they did, they would not get a second opportunity.