One of the things that I was told when I was starting out was to spend extra money on suits and shoes (things that can be seen and will last and last) and save money on socks, underwear and shirts (which wear out and aren't necessarily seen - shirts being the exception there when you take your jacket off).
I was reminded recently to always keep a pair of new black dress socks off to the side in your sock drawer for interviews or other key sessions where a new pair would be important. This could include when you might have to take your shoes off, and therefore eliminate worry about worn socks showing.
judging by this thread, I've been doing it wrong!