Ten or twenty years ago, I would have sworn up and down that a two pairs of socks combination was the only way to go, plus one pair for spare (like if I stepped into a river). The skin on my feet has changed now, so a single pair of thick socks is good, plus a pair for spare.
For summer, I would never take so many under layers. But that is just me.
I always carry some rain pants. For one thing, if I need to rinse out my hiking pants, I can wear the rain pants while they dry. Or, they can provide extra warmth or even rain protection should it really pour down rain.