It seems to me one should dress for the activity. An easy hike, on a somewhat busy trail, is a common first date in my area. Weirdly, even in winter.
So, dressing for the trail would be appropriate, and different from, say, wandering a museum, a movie, or simply lunch.
I’m out of the dating pool, but (somewhat) locally, I’d be up for a jeans and nicer top sort of thing at the arcade in Manitou Springs. Outdoor, walkable to many other options.
Same with heading uphill to the Carousel of Happiness, or even wandering a mountain town.
The idea is casual conversation, no pressure, a reasonable means of escape if it goes weird, a variety of input to steer conversation.
Clothes are to highlight you while being practical.