I don't belong to a gym. We live in an urban area and are within walking distance of grocery store, drug store, cobbler, dry cleaner, etc, etc. I often motivate myself to go for a walk by combining errands with the task, killing two birds with one stone. In fact, my dentist has never seen me in anything but gear, because her office is exactly 1.5 miles away.
Technically, I could walk these errands in ballet flats or cons and jeans, and I have done that too, particularly if DH is joining me and we are planning to pop in somewhere for lunch or dinner during our loop. But it's not as comfortable and I am loathe to walk too briskly, work up a sweat and muss my nice clothes.
If the errand requires a car, then I change out of gear, no matter how brief the errand, no matter if I come right back home and change back into gear. It's funny but I often feel foolish for changing just because I'm getting in the car! I used to dress up just to pick the kids up from school or their friends' houses ... even if I wasn't even getting out of the car. Then again, I also still have a mental block about wearing gear to an airport. My mom taught me to dress nice when going to an airport (even if you are just picking someone up and not flying).