Mission select:
Press X, L2, Triangle, R2, Select at the title screen.

Invincibility:
Pause game play, then press L1, R2, L2, R1, Select.

All quick missions:
Press R1, L1(2), R1(3) at the title screen.

All special features:
Press L1, L2, R1, R2, X, Select at the title screen.

All Weapons:
For all weapons, unlock each specialist at least once in Campaign mode.

Campaign Bonuses:
To unlock it's corresponding bonuses successfully complete Campaign mode on the Veteran setting (There is no need to play on the Elite difficulty setting to unlock anything).