I went from ORD to HNL once in sandals. My feet FROZE. Never again.
Socks, for me, are a must. And unlike my 7th grade math teacher, I won't wear socks and sandals.

So I do slip on shoes, like the Merrill Barefoot Life Slant Glove. Pop them on and off when I want, but always have clean socks on. Never barefoot again when traveling.