Darn Tough wearers - How does the quality compare to Smart Wool? I wear synthetic wool socks year-round (super sweaty feet - only things keeping my shoes from being swamps) and can burn out a pair of Smart Wool in about 2 years, and the less expensive Sam's band synthetic/merino wool socks in about 9 to 12 months.
I think Darn Tough socks are more durable, but wick less well than Smartwool. The extra durability seems to come from the increased synthetic, which traps moisture.
The very best socks I own are a couple pair of thin wool socks from Patagonia (10+ years old, from back when they made socks), and some Filson over-the-calf boot socks (also no longer made).
To the larger question, I'll concur with those who have advocated spending a bit more on denim. The environmental impact of denim made in the developing world is atrocious from everything I've read. I'll pay a few more bucks for denim that's dyed in the US or Japan if for no other reason than it's not turning some poor person's drinking water blue.
For boots, I'll agree with others that the Red Wing Heritage series is great. Also, my experience is that the made in Oregon Danners are still high quality.
For shoes, I also like Allen Edmonds, but my favorites are from Alden. Yeah, they're expensive, but I've bought several pair lightly used on eBay for very little.
Someone above mentioned Brooks Brothers dress shirts, which are my go-to as well. But, I'll add that the Stafford dress shirts from J.C. Penney's are way better than they should be for <$20, and better than what I've seen from LL Bean and J. Crew the past couple years.
But at least as much as the quality of the garment matters for longevity, I think figuring out an enduring fit is at least as important. I have a couple pair of pants from about 10 years ago at the height of the skinny fit trend that today just look dated. I doubt I'll ever manage to wear them out. There's a middle of the road slim-ish, straight-ish fit that would have fit right into a LIFE magazine shot in 1965, or a Ralph Lauren ad from 1985, or a J.Crew cover from 1995 that just seems to be enduring, and that's what I try to shoot for to make high quality clothes wearable for the long term.