Honestly, the only reason to wear a flight suit off base is if you're on a cross-country or out-and-in. Why is this a big deal. If you really need to stop on the way home, have a pair of shorts and a t-shirt at the office.
Yes, I've jammed in and out of ATMs and occasionally a gas station before I ran dry, but if you're in one place long enough to get hassled, you've already exceeded the "brief and essential" stop rule, which, by the way doesn't exist in Marine land. I lived in Jacksonville, North Carolina, for 13 years without getting hassled once. If someone is getting hassled for wearing a bag, I have no sympathy. It's your own fault and you're doing it wrong.