No matter what socks you wear, carry moleskin and Bandaids to cover tender spots before they get out of hand. On walk day, the major early morning decision is . . My solution is a pair of shorts with zip-on pant legs. If you expect cold weather or fear heavy brush or poison oak, this combination is invaluable. I bought a pair 10 years ago before hiking the John Muir Trail, wore them for three weeks and have used them ever since.
Several varieties are now available at major sporting goods stores.
I like cotton in summer and a light wool blend or a sweatshirt over a cotton T-shirt in winter. Any shirt will do as long as it fits loosely and is comfortable. I have two, one lightweight and the other heavier. If I could carry only one extra item of clothing, it would be a windbreaker. Since most of my hiking is during periods of good weather, I prefer a pullover polyester shell.