The clothing brand I've had the best experience with in terms of longevity is Patagonia. I have some items that are passing the 20-year mark now, things I wear every year like Hawaiian shirts in the summer and fleece gloves and insulated jackets in the winter. In the few instances where a piece has failed sooner than I expected, they repaired or replaced it.

In terms of longevity in outerwear, one of things I look for is nylon fabric. A lot of brands (including Patagonia) are using polyester more for jackets, bathing suits, etc. There are some advantages, like it holds DWR treatments better, and can be made with recycled plastic. But in terms of durability there is no comparison; nylon is just tougher gram for gram.

For socks, wool hiking-style socks seem to last well for me. By hiking-style, I mean the socks have different "zones" of thickness, usually thicker on the sole and heel, thinner across the top and ankle. I have Wigwam hiking socks and Smartwool dress socks have lasted well; in fact I'm having trouble remembering if any of them have actually worn out. Mostly they just get slightly thinner over time. I have tried a bunch of cotton socks, and Gold Toe seemed the most durable, but I still like the wool padded style better.