Regular clothing for short trips.

"Anyone else find that the nice expensive clothes are not really necessary for a 2 or 3 day trip, weather permitting?"

I use a thrift store dress shirt (65/35 blend) for my backpacking trips
$10 nylon shorts
Target socks
A surplus boonie hat
…and so on. You get the idea.

Still alive. :)

Wrote this a while ago. May give some ideas:
http://www.pmags.com/300-gear-challenge

In many instances my regular clothes are my hiking clothes, with one major exception: I never wear jeans hiking. I find for hiking jeans are either too hot (when it's warm out) or too cold (when it's cold or wet or both out) and they are restrictive and chafe. And, of course, they take forever to dry out. However, much of my "everyday" clothing qualifies as hiking clothes by default. I wear Merino wool often, not just when hiking, and have probably 10 Merino shirts in my closet. I wear wool socks nearly every day, also (I work in a cold office). So about the only thing that changes for me is my choice of leggings. I do tend to use some version of nylon hiking pant, but have used yoga pants before (they hold water, though) and also running pants (which I believe are nylon). I have a number of hiking buddies that wear jeans or yoga pants also.

Yes, when your "regular clothes" are comfy outdoor clothes, that helps! Same here with lots of Merino, wool in general in winter.
I also use clothes that I had bought for backpacking as daily wear, particularly in winter.
Shoes are the main difference between what I wear hiking and every other day.

Yes.
I have worn jeans while backpacking many, many times. They protect my legs from thorny weeds and brush better. And they are cheap to replace.
I almost always wear a cotton shirt. I find synthetic shirts to my stifling in anything above 60 degrees and I don't find cotton shirts to be a problem in cooler winter weather either.
Cotton button up shirt, jeans, sneakers, mesh hat, and my gear shoved into am old jansport school backpack is my standard summer kit. I do not look like a backpacker.

Of course I understand the limits of that clothing. I find that I mostly end up hiking in dry weather with a predictable forecast. I know how to dress in wet weather.

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In Alaska, I can't be sure of sunny days, so while I'll wear cotton street clothes for some day hikes, for overnights, it's always polypro, nylon, polyester, etc. Having clothes I can depend on if they get wet, ups my safety and/or lowers my pack weight because I need less back-up clothing.

Only in the last few years have I gone totally dry-while-you-wear-it having previously used cotton briefs and t-shirts because I liked it against my skin. Only in winter would I have polypro long underwear as a base layer. Since I've found some synthetic t-shirts and underwear that fits decently and feels fine, I'm really liking how much drier I hike (the sweat evaporates). In cold climates, I like the Inuit wisdom of "Never sweat" or more completely, "Never let your clothing get wet with sweat – reduce your clothing or exertion level BEFORE you get soaked with sweat." I find it much more comfortable and it improves safety to not get caught with sweat-soaked clothing if the wind comes up just as you finish the uphill or, more so, you get injured.

In hot weather to the south, yeah, I use a lot of beater cotton clothing. I've got a box marked, "Road trip and field clothes" that gets the worn office and casual clothes. Then when I have a desert hike or will be doing a system installation (plumbing, wiring, etc); I bring those old clothes. I especially like it when it is on its last legs, because I fly out with it, but throw it away as I go, having less and less as the week goes on.