Remap Caps Lock to Control

Open System Preferences

Then go to Keyboard - Modifier Keys...

keyboard

Remap Caps Lock to Control, then OK.

remap

Use Option as Meta key

For system terminal users:

system

For iterm terminal users:

iterm

Use Meta key in Global

Use DefaultKeyBinding.dict to set custom key binding.

There is a Keybindings for emacs emulation from hcs.harvard.edu.

wget -O- http://www.hcs.harvard.edu/~jrus/site/KeyBindings/Emacs%20Opt%20Bindings.dict > ~/Library/KeyBindings/DefaultKeyBinding.dict

Learn more

Advanced

If you want more deep custom, use Karabiner.